Preheat the oven to 350 degrees F. As it heats, fry the turkey bacon. Once it's fully cooked, set the bacon aside on a plate lined with paper towels.
Dice the onion and cook it over medium heat with the chiles, so the onions absorb some of the flavor. Cook for about 4-5 minutes, or until the onions are translucent. Set aside.
Crack the eggs into a mixing bowl. Add the milk and season with salt and pepper, whisking everything together until fully combined. Pour the egg mixture into the muffin tin, filling each cup only halfway.
Crumble the bacon, distributing it to all of the egg-filled muffin cups. Spoon in the chiles and onion, then sprinkle each one with cheese.
Cook for 25-27 minutes, or until eggs have set and are no longer runny.
Recipe by Collegiate Cook at https://collegiatecook.com/2014/09/10/bacon-cheddar-frittata-cups/