Soak the bread pieces in milk for about 10 minutes. Shred the bread into small pieces.
Mix ground chicken with egg, mayonnaise, and bread. Mix in onion and season to taste.
Preheat oil in a frying pan over medium heat. Spoon equal portions of the meat mixture into the pan, leaving a little bit of space between each patty. Fry on each side until golden brown (about 4-5 minutes on each side).