Separate the egg yolks from the whites. Reserve the yolks for another use.
Beat the egg whites until they are a little frothy. Add salt and pepper, about a 1/2 teaspoon of each.
Chop the tomatoes, spinach, and olives to your desired size.
Heat the olive oil in a nonstick or cast-iron skillet over medium heat.
Reduce the heat to low. Pour the egg whites into the pan and swirl them around until the egg whites completely coat the bottom of the pan.
Use your spatula to pull the egg whites to the center, exposing parts of the pan and allowing the egg to fill the exposed parts so that it cooks completely.
When the egg has almost set, add the chopped tomatoes, spinach, and feta cheese to one-half of the omelet.
Fold the other half of the omelet over the filling. Cook for another 30 seconds to 1 minute, or until the filling is warmed through.
Use the spatula to help slide the omelet out of the pan. Serve immediately and enjoy.
