- Preheat your oven to 375°F (190°C). Thoroughly grease a 12-cup muffin tin with cooking spray or line with silicone muffin cups for easier removal. 
- Wash and chop all vegetables to similar small dice sizes (approximately 1/4 inch pieces) to ensure even distribution and cooking. Blot excess moisture from tomatoes and spinach with a paper towel to prevent your egg cups from becoming soggy. 
- In a large bowl, whisk eggs and milk until fully combined and slightly frothy. Season with salt and pepper. 
- Fold the chopped vegetables and herbs into the egg mixture. Be gentle to maintain the air you've incorporated during whisking. Reserve about 2 tablespoons of cheese for topping. 
- Using a 1/4 cup measuring cup or ladle, fill each muffin cup about 3/4 full with the egg mixture. This allows room for expansion while baking. Distribute the vegetable pieces evenly among cups. 
- Sprinkle the reserved cheese on top of each egg cup. 
- Bake for 20-22 minutes until the centers are set and the tops are slightly golden. They should spring back lightly when touched. 
- Allow to cool for 5 minutes before removing from the tin.