My husband grows flats of greens spouts (baby greens) that go into the enclosure. You could easily sprout containers of greens under a lamp and cycle them in. They come up pretty quickly. I've tried with varied success:
Greens (collard, mustard, turnip, kale, lettuce mix) - older transplanted sprouts worked best, the seedlings got trampled, need extra light to grow. They are still doing well, and have held up to a fair bit of abuse. They will tolerate low light but won't thrive. I have an LED flood light over mine, a basking light isn't enough.
Clover (seeds, transplanted seedling and grown transplants) - spouts got trampled and dried out. Not enough light. Didn't water enough. The grown transplants were rather unsightly.
Nasturtiums - need extra light, but seem ok.
Ginger root - slow so far, but it sprouted.
Wheat Grass - not enough water (?) and gets floppy.
Peas - never sprouted
I'm sure you could find seeds for a culinary variety of dandelion that had more and fuller leaves.