Preheat your oven to 350°F (175°C). This step is crucial for ensuring that your muffins rise beautifully and cook evenly.
Lightly grease a muffin tin with cooking spray or line it with muffin liners. This will prevent the egg muffins from sticking and make for easier cleanup.
In a mixing bowl, combine the 5 egg whites, 2 large eggs, and 1/4 cup of skim or almond milk. Season with salt and pepper to taste. Using a whisk, beat the mixture until it is well combined and slightly frothy.
Fold in the chopped green onion, fresh kale, roasted red peppers, and crumbled feta cheese into the egg mixture. Make sure the vegetables are evenly distributed for a burst of flavor in every bite.
Pour the egg mixture evenly into the prepared muffin tin, filling each cup about 3/4 full. This allows room for the muffins to rise without overflowing.
Place the muffin tin in the preheated oven and bake for about 20-25 minutes, or until the muffins are set and lightly golden on top. You can check for doneness by inserting a toothpick in the center; it should come out clean.
Once baked, remove the muffin tin from the oven and let the muffins cool for a few minutes before gently removing them from the tin. Serve warm or store them for later!