Preheat oven to 350°F and spray cooking spray in a muffin pan. Set aside.
In a large bowl, use a whisk to beat the eggs until frothy.
Add the shredded cheese and stir to combine. Set aside.
In a frying pan on the stove, cook the onion and bacon over medium heat for about 10 minutes. Add in spinach and stir to combine. Cook for about 3 minutes or until spinach is wilted. Remove from heat and let cool for five minutes.
Add spinach mixture to the egg mixture and stir until thoroughly combined.
Ladle the egg mixture into a muffin pan being careful to not overfill the muffin cups. Cook for 15 minutes.
Remove from oven and let cool for 5 minutes.
To remove the muffins from the pan, use a knife and glide around each muffin until you can gently remove them. Serve immediately.
Video
Notes
Serving recommendations: Top with additional cheese, bacon or spinach before serving.