Creating the Tomato Spinach Frittata is easy when you follow these steps:

1. Preheat Your Oven: Set your oven to 375°F (190°C) to ensure it is hot and ready.
2. Sauté Vegetables:
– In an oven-safe skillet, heat the olive oil over medium heat.
– Add the onions; sauté until they are translucent, about 2-3 minutes.
– Add the chopped spinach and halved tomatoes, and cook until the spinach wilts.
3. Whisk Eggs: In a bowl, whisk together the eggs, salt, pepper, and garlic powder.
4. Combine Mixtures: Pour the egg mixture over the sautéed vegetables in the skillet. Stir gently to combine.
5. Add Cheese: Sprinkle the shredded cheese on top evenly.
6. Cook on Stovetop: Let the frittata cook on the stovetop for about 3-5 minutes until the edges begin to set.
7. Transfer to Oven: Move the skillet to the preheated oven. Bake for 15-20 minutes until the frittata puffs up and the center is set.
8. Cool Slightly: Once done, remove the skillet from the oven and let it cool for a few minutes.
9. Slice and Serve: Use a knife to slice the frittata into wedges, and serve warm.

Following these instructions will result in a beautiful and delicious Tomato Spinach Frittata every time.