Preheat oven to 350 degrees. Generously grease muffin tin with butter, set aside.In a medium bowl whisk together eggs, onion powder, garlic powder, pepper and salt, set aside.
Divide the diced red onion, bell peppers and spinach between the 12 muffin cups.
Pour in the egg mixture filling each cavity 3/4 of the way full.
Bake for 15-20 minutes or until the egg muffins look set. Note they will puff up as they cook and will deflate as they cool. Cool for 2-3 minutes in the pan then remove and serve immediately!
Notes
I highly recommend greasing your muffin tin with butter not cooking spray or oil. I have tried this recipe using all three and butter helps the egg cups release easier and makes for a much easier clean up. Also using a nonstick pan makes a huge difference as well. Here is the non stick muffin tin we use!Spice up these egg muffin cups by adding some diced jalapeño, serrano, or poblano peppers. You could also add a pinch or two of crushed red pepper flakes or cayenne pepper.