In a bowl, whisk together egg, egg whites and milk.
Heat oil in a large nonstick pan over medium-high heat. Spread the oil all over surface of the pan. When oil becomes hot, add eggs. Depending on the size of your pan, you might need more or less of the egg mixture; you want a thin layer that will easily roll up. Swirl the pan around as needed to evenly spread out the eggs. Cover and cook for 1 to 2 minutes.
Gently flip eggs. Cover again and cook for 1 minute.
Carefully remove cooked eggs from the pan and place on a plate.
Using the egg as a tortilla, layer bacon, ham, avocado, potatoes and spinach on top. Roll into a burrito.