Preheat the oven to 350 degrees F (175 degrees C). Lightly grease 2 muffin tins. Line a baking sheet with aluminum foil.
Lay bacon strips in a single layer on the baking sheet. Bake in the preheated oven until browned and crisp, about 30 minutes. Reserve grease. Drain bacon slices on paper towels. Chop into small pieces.
Transfer bacon grease to a skillet. Cook onion in the skillet over medium heat until transparent. Drain on paper towels.
Whisk eggs and milk together in a bowl. Add bacon, onion, spinach, Colby Jack cheese, hot pepper sauce, Italian seasoning, salt, and pepper. Scoop mixture into muffin pans using an ice cream scoop, filling cups 3/4 full.
Bake in the preheated oven until muffins harden at the edges, about 50 minutes.