I've tried just about everything that I have given to the rats, hamsters and the rabbit.
lettuce, peas, cucumber, kale, carrot (not such a good one), apple etc etc. (I gave up finding out what they like from websites and decided on the "try it an see" with a little bit of common sense. for example, i did not put the cat food in the fish tank. did put some of the left over turkey though, they loved it.
I went to tesco and bought a 98p pack of 4 forks. I impale any food onto the fork, tie a thread wih loops to a catch on the hood. drop it in, then later on, pull it out.