Preheat your oven to a cozy 375°F (190°C).
Cook the turkey bacon until it's nice and crisp. Set it aside to cool, then crumble it into small pieces.
Give the spinach a good rinse. Dice the green bell pepper and chop the green onion. If using frozen spinach, make sure it's thawed and gently press out any extra water with a paper towel to avoid soggy muffins.
Lightly grease a 12-cup muffin tin with a tiny bit of butter.
In a medium bowl, crack open the eggs and whisk them until they're well blended and slightly frothy – about two minutes if you have the time!
Add the prepared spinach, cheddar cheese, diced bell pepper, green onion, and crumbled bacon to the beaten eggs. Stir everything together until just combined.
Carefully pour the egg mixture into each muffin cup, filling them about 1/2 to 2/3 full. Don't overfill, or you might have a bubbly mess!
Pop the muffin tin into the preheated oven and bake for 15 minutes, or until the muffins are set and lightly golden.
Let them cool slightly before serving. These are perfect for a quick breakfast or a healthy snack!