Spinach Frittata

This is a quick, easy and cheap dinner. You can leave out the bacon if you are a vegetarian. I have also made it with mushrooms.

6 eggs
¼ cup milk
2 cups cheese, divided
1 small onion, diced
1 box frozen spinach, thawed, drained and squeezed dry
1 can diced tomatoes, drained
6 slices bacon, cooked and cut into small pieces

Preheat oven to 400. Cook onion in olive oil until tender. Add spinach, tomatoes and bacon. Whisk eggs with milk and 1 cup cheese and add to vegetable mixture. Cook until sides become firm. Place in oven and cook for about 10 minutes. Add 1 cup of cheese to top of mixture and cook until firm (shake pan slightly to check if firm). Leave to sit for about 5 minutes. Enjoy!