Crikey, haven't seen Tilapia buttikoferi for years! In the early 80s these were considered real status fish, but notorious for their size, aggressiveness and destructiveness.
Anyway, feeding isn't a problem. Yes, they are omnivores, and in the wild at least they are like most tilapia and feed extensively on soft plants and organic detritus, plus whatever small invertebrates they happen to find. Under aquarium conditions a basic pellet diet should be fine as a staple, but among the green foods necessary to avoid bloating look to things like cooked spinach, cooked peas, blanched lettuce, duckweed and Indian fern. Realistically, pretty much any plant added to the tank will likely end up eaten, so you could try clumps of Elodea, Cabomba, etc. if these are more easily obtained. Some tilapia enjoy cooked rice, but use this sparingly because it's filling rather than nutritious.