If you’re going to use the treat for training I would suggest a treat that can be fed in relatively large amounts without it being bad for the bunny. This means that store bought treats and fruits make bad training treats, as those should be fed very limitedly and thus make for very short training sessions (as they WILL stop cooperating when the treats are gone :’D ). I use pellets of a different brand that have a strong odor as treats (Beaphar Care+). The buns go mad for them and because it’s pellets it can be fed in relatively large amounts without upsetting bunny tummies. I give them 1 pellet as a reward for a task so you can imagine you can train relatively long with them.
I like using them in a hide/seek intelligence game (one of those with doors/slides/knobs they have to try and open. Because of the odor I like to think it’s easy for them to sniff something is under the doors/slides/knobs.
Small pieces of veggie would work well I believe.