Preheat oven to 375 degrees. Coat two 12-hole nonstick muffin pans with cooking spray or use just one pan and cook in two batches.
Combine all ingredients in a large bowl; spoon about 2 heaping tablespoons egg mixture into each prepared hole, making sure to stir mixture after filling each one.
Bake until bottoms are golden brown and muffins are cooked through, about 15 minutes.
Remove pan(s) from oven and let muffins cool for a few minutes in pan(s); Remove muffins to a wire rack to cool more (and repeat with remaining ingredients if necessary).