Cut the chicken breast into small pieces.
Slice the onion and bell pepper into thin strips.
Season the chicken breast with salt and pepper, cook it in a pan, then set aside.
Sauté the onion and bell pepper in the pan.
Place the sautéed vegetables, chicken breast, and mozzarella cheese on a tortilla.
Fold the tortilla in half.
Toast both sides of the quesadilla in a pan until golden brown.
Cut into bite-sized pieces.