Finely chop the chicken breast.
Finely dice the onion and bell pepper.
Mix chicken breast, onion, bell pepper, salt, and pepper to form a patty.
Heat olive oil in a pan and cook the patty on both sides.
Wash and prepare the lettuce and tomato.
Cut the whole wheat mini bun in half.
Layer lettuce, cooked patty, and tomato on the bun in order.
Top with the other half of the bun to finish.