Preheat your oven to 350°F (175°C). Grease a muffin tin with cooking spray or oil.
In a large mixing bowl, whisk together the eggs and milk until well combined.
Add the chopped spinach, diced bell pepper, diced onion, shredded cheese, salt, black pepper, garlic powder, and paprika to the egg mixture. Stir until all ingredients are evenly distributed.
Pour the egg mixture evenly into the prepared muffin tin, filling each cup about 3/4 full.
Bake in the preheated oven for 20-25 minutes, or until the egg muffins are set and lightly golden on top.
Remove from the oven and let cool for a few minutes before carefully removing the muffins from the tin. Serve warm or allow to cool completely and store in an airtight container in the refrigerator.