Is it a baby Oscar? When I got mine I got Roseline sharks to go with it. Since they have grown up together she don't see them as food, well so far anyways. Where as when I put some giant Danios in from my JD tank she promptly ate 2 of them, and still chases the remaining 3.
So if yours is still young you may have better luck. Here 6 months later I still have all my sharks and are keeping pace with her growth.
It's basically an arms race of sorts, needing a fish that will keep up or outpace your fishes mouth/speed.
My sharks have learned to grab up most all the mess Toni makes when she eats
Edit: I forgot to add that my sharks also eat Toni's poop. I know right sounds gross, but they do it, most of the time it will not even hit the bottom of the tank before the sharks eat it all.....