You are feeding vegetable matter to a carnivore and don't understand why it doesn't grow? Holey moley!
pretty much any "prepared food" is going to be mostly wheat and corn products with some fish based protein component, but even that would be a huge improvement over a vegetarian diet.
Seriously, get some fish, chop it up, toss it in. Shrimp, krill, scallops, road kill... anything that is MEAT based will be a vast improvement.