Preheat the oven to 400°F and generously coat a 12-cup muffin tin with cooking spray.
Crack the eggs into a large bowl, season with salt and pepper, and whisk until well combined.
Divide the spinach, feta, tomatoes, onion, garlic powder, and dried basil among four muffin cups; divide mushrooms, sun-dried tomatoes, white cheddar, and Italian seasoning among four more; divide bacon, cheddar, broccoli, and garlic powder among the final four.
Pour the egg mixture over the fillings until each cup is about two-thirds full. Do not fill to the top because the eggs expand as they bake.
Bake for 13 to 15 minutes, until the centers are set and no longer look wet.
Cool in the pan for 5 minutes, loosen the edges with a butter knife, remove, and serve.