Preheat oven to 350°F (175°C). Grease a standard 12-cup nonstick metal muffin tin generously with olive oil or nonstick cooking spray (or use silicone muffin liners for effortless release).

Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the minced shallot and diced red bell pepper. Sauté for 3 to 4 minutes until softened and fragrant. Add the chopped baby spinach and cook for 1 to 2 minutes just until wilted. Remove from heat and let cool for 3 minutes.

In a large 4-cup glass measuring pitcher with a pour spout, vigorously whisk together the 10 eggs, whole milk, garlic powder, dried oregano, kosher salt, and black pepper for 60 seconds until frothy, aerated, and completely smooth.

Divide the sautéed spinach, red pepper, and shallot mixture evenly among the 12 greased muffin cups (about 1 generous tablespoon per cup).

Drop crumbled feta cheese evenly into each cup over the vegetables. Slowly pour the whisked egg mixture into each cup, filling each about 3/4 to 7/8 full. Lightly sprinkle the grated parmesan cheese across the tops.

Bake at 350°F (175°C) for 20 to 22 minutes until the egg muffins are puffed, set in the center, and the edges are lightly golden brown.

Remove from the oven and let the tin sit on a wire rack for 5 minutes (they will naturally settle slightly as they cool). Run a small silicone spatula or butter knife around the edges to release the muffins onto a serving plate. Serve warm!