I need to order from a menu where both chicken cubes and ground chicken are choices. What's the difference?
Ground chicken (or any other ground meat) has been ground with a grinder. It can be formed into patties (like hamburgers), balls (like meatballs), sausage and so on, but if cooked as-is will tend to turn into crumbles.
Cubes are, well, meat cut up into cubes: chunks of whole meat, with the original texture.