Preheat your oven to 350°F and lightly grease a 12-cup muffin tin with cooking spray or butter. This prevents sticking and ensures beautiful golden edges that look bakery-perfect.
Whisk together 12 large eggs and 1/2 cup milk in a large mixing bowl until completely combined and slightly frothy. Season with salt, pepper, and garlic powder, stirring to incorporate every spice evenly throughout the mixture.
Gently fold in all diced vegetables, chopped turkey, cheddar cheese, and fresh parsley into the egg mixture, being careful not to deflate the eggs. Divide this filling evenly among the 12 muffin cups, filling each about three-quarters full to allow room for rising.
Bake loaded breakfast egg muffins crowd-pleasing portions for exactly 23 to 25 minutes until centers are set and edges are lightly golden. A toothpick inserted into the center should come out clean with no runny egg remaining in any cup.
Remove the muffin tin from the oven and let cool for 5 minutes before carefully running a thin knife around each cup's edge. This simple step prevents tearing when you pop them out of the pan for serving.