Preheat oven: Preheat your oven to 350°F (175°C). Grease an 8x8 inch square baking pan.

Whisk eggs and milk: In a large bowl, whisk together the eggs and milk until well combined.

Add ingredients: Stir in the shredded cheese, spinach, tomatoes, red onion, green onion, salt, and pepper.

Pour into pan: Pour the mixture into the prepared baking pan.

Bake: Bake for 20-25 minutes, or until the frittata is set and the edges are golden brown.

Serve: Let the frittata cool in the pan for a few minutes before cutting into squares and serving.

Tips:

You can add other ingredients to your frittata, such as bacon, sausage, mushrooms, or peppers.

For a fluffier frittata, let the egg mixture sit for a few minutes before baking.

Serve the frittata with your favorite breakfast or brunch toppings, such as avocado, salsa, or sour cream.

Enjoy your fluffy and flavorful frittata!