Prep the veggies: Dice avocados and tomatoes, and chop the spinach.
Heat the pan: Add olive oil to a non-stick skillet over medium heat.
Cook spinach: Sauté spinach for 1–2 minutes until wilted. Remove and set aside.
Cook egg whites: Pour in egg whites (3 per omelette). Let them set for about 1–2 minutes.
Add fillings: Place ¼ of the spinach, avocado, and tomato on one side. Season with salt and pepper.
Fold and finish: Gently fold the omelette and cook another 30 seconds. Slide onto a plate.
Repeat: Make 4 omelettes total.