I feed my tort on just the slate tile and it works best for both of us. Many torts have difficulty eating from a plate as they want to climb right on top of the food to be able to use their front arms to hold it down. In the wild it would still be growing out of the ground, so it's actually tougher for them in captivity to be served the already cut greens.
Does he usually just put his arms up on the lip of the plate and eat that way? It looks like you have a tile right under it. I would just remove the bowl/plate and give him more space.
Beautiful little guy and definitely cute in his bowl. Mine do it with or without a bowl; I think it's the foraging factor. When I watch them outside, they'll walk a few steps, ignoring what they see, then plop down on top of some flowers to eat other flowers just like them.