Place a tortilla in a dry, hot pan. Layer over some onion, green pepper, and chicken. Scatter all over with a generous amount of cheese, filling all the way to the edges.
Top with another tortilla and press down.
Cook for 3-4 minutes until the cheese has melted and the tortilla has browned on the bottom.
Use a large spatula to flip the quesadilla until toasted on the other side. Cut into wedges and serve with guacamole and salsa.