Spring mix is a ready made salad variety. Usually has about 6 different types of greens/baby lettuce/radicchio, etc... good mixture.
Check your produce isle. It will either be in bags or clear plastic tubs.
Yes, they may come from a desert type environment but they don't spend their lives in the driest part of that environment. They live in burrows that are very humid. Your tortoise needs the humidity or at least a humid area that it has access to. I've been breeding greek tortoises for many years...
Here you can see the difference in coloration between the Jordanian and the Turkish Ibera babies. These are both new hatchlings just a couple of days old.