Hello!
Probably, hibiscus and opuntia cactus can be a good start. Mulberry and grape leaves are seasonal but good. Endive and rocket salad (ruccola) are fine staple greens too. Dandelions, coriander leaves are good addition. Squash, pumpkin and watermelon provide good shade and leaves and fruit can be fed too.
In fact, variety works better than just a few staples and as you plan to grow your own greens - it makes sense to get more different seeds or ready tortoise seed mixes. The more variety you offer to a baby tortoise the easier it will be to feed him later.