Preheat and Prepare: Preheat your oven to 350°F (175°C). Generously coat a standard muffin tin with olive oil spray to prevent the eggs from sticking.

Whisk the Base: In a medium mixing bowl, vigorously whisk the eggs, milk (if using), garlic powder, salt, and black pepper until the mixture becomes fluffy and frothy.

Add the Mix-ins: Stir the finely chopped spinach and diced red bell pepper directly into the whisked eggs until evenly distributed.

Fill the Muffin Cups: Divide the egg and vegetable mixture evenly among 6 greased muffin cups, filling each cup about 3/4 of the way full.

Add Feta: Evenly sprinkle the crumbled feta cheese directly over the top of each filled cup.

Bake: Place the tin in the preheated oven and bake for 20 to 25 minutes. The muffins should look puffed, golden on the edges, and firmly set in the center.

Cool and Unmold: Let the muffins cool in the tin for 5 minutes. Gently run a thin knife around the outer edges of each muffin to release and remove them.