The peculiar detail of the image is the round stage with double-paneled backdrop. The two panels radiate from the center of the circle at a 120 degree angle and define a triangular area where the actors are positioned. There is a third panel hidden beh ind the visible two, and the stage is thus divided into three such acting areas. Scene changes may be accomplished simply by rotating the stage 120 degrees either clockwise or counter-clockwise. The device is called by its Greek name, periakton, an d is described by Pollux at Onomastikon 126. 131, and by Vitruvius at De Architectura 5.6.8.
The theatrical equipment confirms that the subject is dramatic. Three ludiones, or dancers perform a stylized dance on what appears to be a military theme. The first is visible in the rear left. Clasping the neck of a horse, this dancer's motion s seems to be highly acrobatic. The trio is completed by the two female dancers in the foreground, armed with helmets, and in the case of the figure on the right, with a shield and small dagger. Mimetic roles are played by the two actors (histriones) at the center of the composition, of which the figure on the right has been identified as an adolescent boy; the one on the left a slave. The figure off stage and to the far left may or may not be associated with the dramatic action.
The image of the histrio, often associated with effeminacy and sexual passivity, is regularly used as a pejorative caricature of excessively dramatic oratorical displays.

Image from: Olga Elia. "Rapresentazione di un Pantomimo nella Pittura Pompeiana" in Gli Archeologi Italiani in Onore di Amedeo Maiuri. Cava dei Tirreni: Di Mauro, 1965; p. 178, fig.1.
This under-studied wall is also published in:
Moorman E. M. "Rappresentazioni teatrali su scaenae frontes di quarto stile a Pompei." BAAP I (1983): 73-117
From Apuleius's other work, the Metamorphoses, we receive a description of a pantomime display that resembles closely the dramatic structure of the above image.
Apulieus Metamorphoses 10.29:Dies ecce muneri destinatus aderat. Ad conseptum caueae prosequente populo pompatico fauore deducor. Ac dum ludicris scaenicorum choreis primitiae spectaculi dedicantur, tantisper ante portam . . . subinde curio sos oculos patente porta spectaculi prospectu gratissimo reficiens. Nam puelli puellaeque uirenti florentes aetatula, forma conspicui, ueste nitidi, incessu gestuosi, Graecanicam saltaturi pyrricam dispositis ordinationibus decoros ambitus inerrabant nunc in orbem rotatum flexuosi, nunc in obliquam seriem conexi et in quadratum patorem cuneati et in cateruae discidium separati. At ubi discursus reciproci multinodas ambages tubae terminalis cantus explicuit, aulaeo subErat mons ligneus, ad instar incliti montis illius, quem uates Homerus Idaeum cecinit, sublimi instructus fabrica, consitus uirectis et uiuis arboribus, summo cacumine, de manibus fabri fonte manante, fluuialis aquas eliquans. Capellae pauculae tondebant herbulas et in modum Paridis, Phrygii pastoris, barbaricis amiculis umeris defluentibus, pulchre indusiatus adulescens, aurea tiara contecto capite, pecuarium simulabat magisterium. Adest luculentus puer nudus, nisi quod ephebica chlamida sinistrum tegebat umerum, flauis crinibus usquequaque conspicuus, et inter comas eius aureae pinnulae colligatione simili sociatae prominebant; quem [caducaeum] et uirgula Mercurium indicabat. Is saltagradum scitule referens e conspectu facessit. Insequitur puella uultu honesta in deae Iunonis speciem simil is: nam et caput stringebat diadema candida, ferebat et sceptrum. Inrupit alia, quam pu tares Mineruam, caput contecta fulgenti galea-et oleaginea corona tegebatur ipsa galea-clypeum attollens et hastam quatiens et qualis illa, cum pugnat.The day for the performance arrived. I am led to the seating area while the public follow in festive delight. Since the first part of the festival was devoted to choral festivities, I stood outside . . . and delighted my curious eyes through the open door at the sight of the spectacle. Girls and boys in the youthful prime of life, preeminent in beauty, in shining clothes, with expressive step, in order well disposed, wandered in graceful patterns, ready to dance a Greek pyrriche, now bending into a moving circle, now lining up in an oblique row and forming a hollow four-sided wedge, then separating into groups. But as soon as the final blare of the trumpet brought an end to the intricate twists and turns of their to-and-fro movement, the curtain was drawn up; the siparia were folded together and the stage building set-up. It was a wooden mountain, on the model of that famous mountain that the prophet Homer hymned as Idaean, constructed on a high scaffolding, planted with bushes and live trees, pouring out a stream of water from the very top, a fountain flowing by the workmanship of a carpenter. A few goats grazed on the grass, and a young man, nicely tunic-clad in the manner of Paris, the Phrygian shepherd, a flowing cloak flowing from his shoulders, played the master of the flock, his head covered with a golden tiara. A handsome boy was there--his only covering an ephebic tunic over his left shoulder, notable for the yellow hair that fell all around, and among his hair stuck up little wings of gold, joined by a similar bond; caduceus and rod showed him to be Mercury. He danced forward with a gold-plated apple in his right hand, and offered it to him who looked to be Paris, while he indicated the wishes of Jupiter with a head movement; then he withdrew elegantly and disappeared from sight. There followed a girl with noble features, in appearance like the goddess Juno, for a splendid diadem bound her head. Another girl burst in who you would take for Minerva, her head covered with a brilliant helmet, and the helmet itself was covered with an olive wreath; she lifted her shield and swung her spear, and was just like the shows herself when she fights. (Translation: Slater and Csapo. The Context of Ancient Drama. Ann Arbor: University of Michigan Press, 1995; pp. 384-5)
The following passage from Apuleius's Florida exhibits the typical contrast between the theatrical and the oratorical performance:
Apuleius Florida 18:Tanta multitudo ad audiendum conuenistis, ut potius gratulari Karthagini debeam, quod tam multos eruditionis amicos habet, quam excusare, quod philosophus non recusauerim dissertare. nam et pro amplitudine ciuitatis frequentia collecta et pro magnitudine frequentiae locus delectus est. praeterea in auditorio hoc genus spectari debet non pauimenti marmoratio nec proscaenii contabulatio nec scaenae columnatio, sed nec culminum eminentia nec lacunarium refulgentia nec sedilium circumferentia, nec quod hic alias mimus halucinatur, comoedus sermocinatur, tragoedus uociferatur, funerepus periclitatur, praestigiator furatur, histrio gesticulatur ceterique omnes ludiones ostentant populo quod cuiusque artis est, sed istis omnibus supersessis nihil amplius spectari debet quam conuenientium ratio et dicentis oratio.Such a multitude of you have come for the purposes of listening, that I think I should rather applaud Carthage, because she has so many friends of learning, than apologize, because as a philosopher I do not decline the opportunity to orate. For this place is chosen both for the greatness of the citizenry when the crown is gathered and for the magnitude of the gathered crowd. Moreover, in an auditorium of this type it is proper to behold neither a floor of marble, nor a decorative wooden stage-front, nor the colonnade of the stage, nor the projection of the high roof, nor the brilliance of ceiling panels, nor the wide arch of the bleachers, nor what this mime utters with wandering mind on other occasions, nor what the juggler purloins, nor what the actor gesticulates, nor what all the other players show to the audience depending on the craft of each; but all of these things should be steered clear of, and nothing more should be beheld than a reasoned gathering of men and the speaker's oratory.