If you haven’t already chop onion, tomatoes and spinach and set aside.

Heat the olive oil in a small non-stick over medium heat.

Once the pan is hot, add onion and saute for 2-3 minutes, stirring occasionally.

Add tomatoes, spinach, salt and pepper and saute for 1-2 more minutes.

Pour the egg whites over the veggies, tilting the skillet until they completely coat the bottom of the sillet.

Once the edges start to set, reduce the heat to medium-low and use a spatula to lift the edges of the omelet, while tilting the skillet to expose parts of the pan to let the runny egg whites fill the bottom of the pan so it cooks completely. This takes about 7-8 minutes for the egg whites to fully cook through.

Once the bottom of the omelet has cooked and there aren’t any more runny egg whites on top, add parmesan cheese to one half and carefully fold the omelet over.

Slide the omelet onto a plate and serve immediately, adding additional salt and pepper to taste.