I like nls, hicari, omega one as the staple for all of my cichlids. As treats for the oscars i;ve kept, i've used garden worms, nightcrawlers, crickets, meal worms(one to two a week), roaches, grass hoppers, other baby cichilds i had to cull, frozen shrimp or krill, freeze dried krill, and sometimes tilapia fillets from the store. Pretty much anything fish safe, never gold fish though.
there's more i've fed oscars but i can't think of anything else right now.