Cut the chicken breast into bite-sized pieces.
Finely chop the tomato and onion.
Stir-fry the chicken breast in a pan with oil.
Add the tomato and onion and stir-fry together.
Place a tortilla on the pan and spread the cooked ingredients evenly.
Top with mozzarella cheese and cover with another tortilla.
Cook until golden brown on both sides.
Cut into pieces for easy serving.