Too much protein? Not sure why you are concerned about this, cats are carnivores they should be eating protein. That is what they use to get their energy and develop their muscles from.
Not sure if you are only
feeding baby food or cooked ground turkey, but that is not nutritionally complete for a cat.
The best way to get your cat to gain muscle mass is to have your cat on a raw diet, period. I have seen it happen over and over again. My senior Puddles is one example, my many foster kittens who go from starving to raw back to kibble (kibble makes them loose muscle mass) when they go to the shelter for adoption. Not even canned food (Wellness kitten) was able to develop the muscle mass that an appropriate prepared raw diet does.
Here is a great website on cat nutrition, it is long reading, but well worth the education:
Here is another website on raw feeding: