My family loves spaghetti but I always make too much pasta. This is a great way to use that extra pasta. It's also a great way to get those vegetables into picky eaters. My kids love it because it's so cheesy.
Preheat oven to 425 degrees (F). Warm oil in a 10 inch nonstick skillet over medium-high heat. Add onion, zucchini, squash and mushrooms. Cook for 2- 3 minutes, stirring. Add garlic, tomato and spinach and cook and additional 2 - 3 minutes, stirring, until spinach wilts. Add optional shrimp or chicken. Season with salt and pepper. Toss in spaghetti and mix thoroughly so vegetables and pasta are evenly distributed.
Whisk mile, shredded Parmesan, 1 tsp salt and 1 tsp pepper with eggs. You can add other spices. I like pepper flakes. Pour egg mixture into skillet and swirl to coat vegetables and spaghetti with mixture. Cook 1 minute, stirring until eggs begin to set on the bottom of the skillet. Pour into a 9X9 pyrex dish, sprinkle with mozzarella cheese on top and place in oven. Bake until eggs have set in center. 10 to 12 minutes. Turn on broiler to high and broil frittata until golden brown on top, 1 to 2 minutes. Watch carefully to prevent it from burning.
Remove from oven, sprinkle with basil, cut into squares and serve.