Preheat your oven to 350°F (175°C). Grease a muffin tin with cooking spray or line it with muffin liners.

In a mixing bowl, whisk together the egg whites and whole eggs until well combined.

Stir in the chopped spinach, sun-dried tomatoes, Italian seasoning, salt, and pepper into the egg mixture. Mix until all ingredients are evenly distributed.

Pour the egg mixture evenly into the prepared muffin tin, filling each cup about 2/3 full.

Sprinkle the crumbled feta cheese evenly over the tops of each muffin cup.

Bake in the preheated oven for 20-25 minutes or until the egg muffins are set and slightly golden on top.

Once done, remove the muffin tin from the oven and allow the egg muffins to cool for a few minutes before carefully removing them from the tin.

Serve the Spinach, Feta, and Sun-Dried Tomato Egg Muffin Cups warm as a nutritious breakfast or snack option.