Cut the chicken breast into bite-sized pieces.
Slice the onion and bell pepper into thin strips.
Heat olive oil in a pan and stir-fry the chicken breast.
When the chicken is almost cooked, add the onion and bell pepper, and stir-fry together.
Season with salt and pepper.
Place the chicken breast and vegetables on a tortilla and roll it up.
Lightly grill the burrito on a pan or grill to finish.