Set oven rack 3 to 6 inches from the heat source and preheat the oven’s broiler.
Heat olive oil in a 10-inch oven-proof skillet over medium heat; cook and stir onion until soft and transparent, about 5 minutes.
Beat eggs, egg whites, spinach, Parmesan cheese, parsley, salt, basil, oregano, and black pepper together in a bowl; pour over onions. Cook over low heat, gently lifting with a spatula and tilting skillet to let liquid run under cooked parts, until partially cooked, about 10 minutes. Arrange tomatoes and black olives on top of semi-soft frittata.
Broil frittata in preheated oven until slightly browned on top, about 5 minutes. Cut into wedges.