Similar to crickets....I use carrots, sweet potatoes, collard greens, Kale, romaine, dandelion and apples. They tend to eat it all well. I just stay away from high water content fruit like oranges as it makes their wheat bran/bedding soggy and smelly.
I feed them the same thing that I feed the crickets....a wide assortment of greens and veggies with a small amount of fruit.
I have a colony (they reproduce) living in one of my turtle cages...they eat what I feed to the turtles (crickets)...they like the slightly moist soil and I also keep a piece of rotting wood in the cage for them.