How large is the oscar, and how large is the tank?
I currently have three that are approaching 6 inches, which is about half grown on average. They have two rather large sword plants as a test to see if they'll leave them alone. So far they've nibbled them some over the past 3 weeks, but mostly left them alone or 'slept' between them. They seem to enjoy having them.
If you want to feed your Oscar live fish, consider getting a 20 gallon tank and a pair of convict cichlids. That way you have a fairly unlimited supply of convict fry (200-300 every 3-4 weeks, and they grow to good feeding size within 4 weeks) that you can be fairly sure are disease free. Buying feeders from the lfs
is always a risky decision.