Cut the chicken breast into bite-sized pieces.
Season the chicken breast with salt and pepper.
Heat olive oil in a pan and cook the chicken breast.
Wash the lettuce thoroughly and remove excess water.
Slice the tomato.
Lightly toast the whole wheat bread or sandwich bread in a toaster.
Spread mustard or mayonnaise sauce on the bread.
Place lettuce, chicken breast, and tomato on the bread in order.
Top with another slice of bread to complete the sandwich.