Follow these simple steps to prepare your egg white muffins with spinach and tomatoes:

1. Preheat the Oven: Set your oven to 350°F (175°C) to ensure it’s ready when you’re done preparing the ingredients.
2. Prepare the Muffin Tin: Lightly grease a muffin tin with olive oil or cooking spray to prevent sticking. Alternatively, use silicone muffin liners for easy removal.
3. Sauté the Vegetables: In a skillet over medium heat, add a small amount of olive oil. Add the chopped onions and garlic, sautéing until the onions are translucent. Add the spinach and cook until wilted. Remove from heat and set aside.
4. Mix the Egg Whites: In a large mixing bowl, whisk together the egg whites, salt, and black pepper until well combined.
5. Assemble the Muffins: Distribute the sautéed vegetables evenly among the muffin cups. Add a few halved cherry tomatoes to each cup and sprinkle with cheese.
6. Pour the Egg Whites: Carefully pour the egg white mixture into each muffin cup, filling about three-quarters full.
7. Bake: Place the muffin tin in the preheated oven and bake for about 20-25 minutes, or until the egg whites are set and the tops are slightly golden.
8. Cool and Serve: Allow the muffins to cool in the tin for a few minutes before removing them. Serve warm or at room temperature.