In a medium mixing bowl whisk together eggs, egg whites, milk, spinach, tomatoes, green onions, and salt and pepper to taste. Pour egg mixture into an 8” non-stick skillet, place in oven on middle rack. Brush both sides of each pita half with olive oil, place on foil and warm in the oven during the last 2 minutes of cooking time. Cook eggs approximately 15 to 18 minutes or until puffy and just set in the center, but not hard. Sprinkle on the feta cheese and return to the oven for one more minute.
Remove skillet from oven, cut omelet in half and place each half in a pita pocket. Press edges into warm pita and serve immediately.