We've found out recently that turtles will eat just about anything they can get their beaks on. Guppies would be good for your turtle. He'll get tons of exercise swimming after them, and it'll help him build back the muscle mass in his let that he probably lost. You might want to also try supplementing his diet with things high in protein to help the muscle regenerate.
As far as vegetables for him to snack on...
-Carrots would be particularly good for Tank Frank, they usually float, so that will keep atop the water.
-We usually try to stay away from zucchini, the stuff just falls apart and the fibers make a big mess and get caught in the filter.
-Lettuce has little vitamin content
-Pretty much anything green and leafy, like spinach and kale is good. These type veggies are packed with vitamins.
And much to our dismay...crayfish don't make good tank mates, but they do make great lobster dinners for turtles.
