hikari is good. and the frozen krill is good too.
in fact. dont be afraid to give your Oscar a ton of different foods while still young. That will get him accustomed to a varied diet. Oscars do best with a supplemented diet. they grow faster, are healthier and more colorful and are less likely to develope HITH.
Try crickets, earthworms, meal worms, june bugs, white fish like cod, market shrimp (raw), even veggies like peas (skinned).