Whisk together eggs, salt, and pepper in a mixing bowl. Chop green onion, seed and chop tomato and bell pepper, and set aside.
Spray skillet with cooking spray and heat over medium.
Add approximately 1/4 of the egg whites and veggies to the hot skillet. Stir and cook until eggs are fully set, then fold in half and then in half again.
Toast bread; peel and slice avocado.
Add avocado slices and cooked egg to a piece of toast, then top with another piece to form a sandwich. Repeat with all remaining ingredients.