Toast bread and heat a frying pan over medium high. Spray pan with non-stick cooking spray and crack in the egg.
After about 30 seconds, use spatula to gently break the yolk (if you don't want an overly messy sandwich). Flip the egg to finish cooking and turn off the heat.
Season with salt and pepper to taste and top with cheese slice. Remove from the pan and place pan back on medium-high heat.
Cook the ham for about 60 seconds per side then place on top of the egg/cheese.
Spread avocado on one side of the toast and top with onion slices. Spread mayo on the other piece of toast and top with egg/cheese/ham. Enjoy!