Cut the avocado in half, remove the pit, peel, and slice it.
Wash the tomato and lettuce thoroughly, then slice them.
Toast 2 slices of bread in a toaster until the surface is crisp.
Spread mustard or mayonnaise on one slice of bread.
Layer ham, avocado, tomato, and lettuce in order.
Cover with the remaining slice of bread.
Cut the sandwich in half.