Prep. Preheat the oven to 375˚F. Generously grease a 12-cup muffin pan with cooking spray.
Cook the bacon. In a large 12-inch skillet set over medium-high heat, cook the diced bacon until crisp. Remove cooked bacon with a slotted spoon and set aside. DO NOT discard the bacon grease.
Sauté the vegetables. Set the skillet back over medium-high heat and add potatoes and vegetables. Season well with salt and pepper and cook for 6 to 8 minutes, or until potatoes are tender.
Combine. Remove the veggies from the heat and stir in 2/3 of the prepared bacon. Evenly divide and spoon the veggie mixture into the muffin pan; top each with cheddar cheese. Set aside.
Make the egg mixture. Combine the eggs, milk, and parmesan cheese in a mixing bowl and whisk until thoroughly incorporated.
Bake. Pour the egg and milk mixture over each muffin cup. Add the remaining bacon pieces over each muffin. Bake for 15 minutes, or until the eggs are set.
Finish and serve. Remove the egg muffin cups from the oven and let them cool for 5 minutes in the pan before serving.