Preheat oven to 375 degrees f. and lightly spray a 6-cup large muffin tin with cooking spray or wipe with oil.
Heat a medium skillet over medium-high heat. Add chopped bacon, and diced red bell pepper then cook until bacon is crispy and cooked through, stirring occasionally.
Drain off the excess bacon grease and set aside
Meanwhile, in a large bowl, add eggs, milk, mustard powder, a pinch of sea salt and pepper, then whisk well to combine.
Stir in the cheese, chives, cooked bacon and peppers.
Divide the egg mixture between the prepared muffin cups.
Bake in your preheated oven for 15-17 minutes or until the center is set and muffins are puffed.