Slice the ciabatta bread in half.
Wash and slice the tomato and romaine lettuce.
Season the chicken breast with salt and pepper, grill in a pan, then let it cool.
Spread mustard sauce on one side of the ciabatta bread.
Layer the lettuce, tomato, chicken breast, and cheese on top of the bread in order.
Cover with the other piece of bread to complete the sandwich.
Cut the sandwich in half for easy eating.