Gerbils love to dig and forage. I take a paper towel roll cut it in half, and stuff it with timothy hay, and any other fruit or veggie I want them to eat. I also stuff hay and food into left over pasta boxes(recyclable ones). They will shred the box for a nest and eat the food. I have found that they love to work for thier food. I use to use a food bowl, but they would always bury it, so now I use the scatter method. I mix their bedding with timothy hay, shredded white paper and toilet tissue. I scatter their food over the bedding and then give it a quick toss. I wouldnt do this with wet, juicy fruit. But you can do this with diced carrots or small pieces of broccoli. They will find it.
I also take a piece of white paper, put the hay and veggies in the center, and then wad it up and make a ball out of it. They can smell the food and eat through the paper. I hope these ideas help.