I'm also currently feeding my cats Innova Evo. They don't need to eat much because it has a lot of calories and it's very high in protein as you stated before. It sounds like you may be feeding Oscar too much food. Mine barely eat 1/2 cup per day and sometimes a bit less than that. I think I'd try giving him less food before changing his diet. Good luck.

I just looked this food up and it has 612k/cal per cup. Most cats only need around 300 calories and some do well on even less. I bet that this is the reason why Ocsar's been gaining weight.