Prepare two slices of whole wheat bread.
Wash and slice lettuce, tomato, cucumber, and onion.
Cut chicken breast or ham into bite-sized pieces.
Prepare sliced cheese.
Spread mustard or mayonnaise on one side of a bread slice.
Layer lettuce, tomato, cucumber, onion, chicken breast, and cheese on the bread.
Cover with the other slice of bread.
Cut in half for easy serving.