Heat oven to 400 degrees.
Grease pan with butter.
Pulse chicken, onion, salt, and pepper in a food processor until finely chopped. (pulse. If you hold it down it will turn into a rubbery gross mess that you will not want to eat!)
Add chicken mixture to eggs and mayo and stir until combined (I was gonna take a picture as I went along, but seriously, it’s not the prettiest thing at this point.)
Add in cheese and veggies.
Shape into nuggets and roll in bread crumbs.
Bake for bout 18 minutes (turn them over halfway through to brown on both sides)
Can be baked ahead of time and frozen for quick dinners later. If baking from frozen state, bake at 425 degrees for 10 minutes or so.