1. Preheat oven 180°C
  2. Cook spaghetti in a large pot of boiling salted water until tender but firm. Drain and refresh with cold water.
  3. Heat oil in a large non-stick skillet over medium heat. Add onions and cook, stirring occasionally, until golden, 10 to 12 minutes. Transfer the onions to a small bowl and let cool slightly.
  4. Whisk together eggs, egg whites and milk in a large bowl. Stir in the onions, Parmesan, parsley, basil, salt and pepper. Add the spaghetti, feta, vegetables and diced tomato.
  5. Pour into (8 cup) ceramic frittata or pie cooking dish. Spread sliced tomatoes and cheese over top and cook for 30 minutes or until golden brown on top.