Pre-heat oven to 350 degrees F.
Cut up onion and bell pepper into slices.
Heat a skillet over medium heat. Once hot, add a drizzle of oil and add sliced vegetables. Cook until softened, approximately4-6 minutes.
Prepare an 8x8 baking dish with oil or nonstick spray.
In a large mixing bowl, combine eggs, milk, seasonings, spinach and mozzarella and stir to combine.
Once pepper and onion are done cooking, add that to the egg mixture and stir.
Pour the egg mixture into the prepared dish and cook for 20 minutes in the oven. After 20 minutes, check the temperature and finish with a 2-minute broil to brown the top.
Let frittata rest for 5 minutes before serving. Enjoy!
