Add water to a 9x13 baking pan halfway to the top. Place on the bottom rack of the oven. This helps to keep the egg muffins moist and tender while baking.
Preheat the oven to 350℉. Generously grease a 12-cup, non-stick muffin pan with cooking spray, set aside. Alternatively, you can line the muffin pan with silicone muffin liners.
In a blender, combine the eggs, cottage cheese, black pepper, and oregano. Blend until well combined and smooth.
Evenly divide the peppers, spinach and feta cheese amongst each muffin cup. I just eyeball this, trying to make them as even as possible. Each muffin cup will have 2-3 tablespoons of veggies and cheese.
Pour about 1/3 cup of the egg and cottage cheese mixture on top the veggies and cheese in each muffin cup. I like to start with less and then go back to make sure they are fairly even. Each cup should be 3/4 full or a tiny bit more.
Use a toothpick to stir the veggies and cheese a bit. This does not affect the flavor, but it helps to bring them to them to the top as the egg muffins bake, which makes for a pretty muffin cup.
Bake for 20-25 minutes or until the muffins are set and cooked through the center. They will puff up when cooking and then deflate bit as they cool.
Cool for 12-15 minutes. Run a knife along the side of each muffin, remove, and enjoy!