OMG, not one reply! I'm new here so ... anyway do you have lights and vertical space? If you do I would do a hibiscus. The flowers are edible! If you have a green thumb you could split the rootball and insert a half round of wood or a pot so he can hide under the roots.
Hi
Sorry only saw your post now. I do not know turtles however what i do for my torts is to put plants that they can eat into the enclosure. So if you can find the plants that it can eat, plant them. But leave them in their pots when you plant them. And you keep two to three if each plant. That way you can swop them around each week and they can recover and or grow nicely in the sun or outside area. And the ones you have in the indoor enclosure will always be healthy.
Great advice on the swapping out. Given the swapping out idea you could grow many native fruits (strawberry, blueberry, raspberry, currants, lingonberry, Swiss chard, lettuces, etc.)!!!! Exciting stuff!!!