Pre-heat oven to 325 degrees. Spray a 13x18" baking sheet with non-stick cooking spray and set aside.
Heat olive oil or rendered bacon fat in a pan over medium high heat. Once hot, add shallot and bell pepper and sauté until softened and fragrant, 3-4 minutes. Add baby spinach and toss with shallot and bell pepper. Sauté for 2-3 minutes, continuously moving around the pan, until spinach is softened and bright green. Dump spinach mixture onto a paper-towel lined plate and set aside.
Add whole eggs into a bowl with milk, salt, and pepper. Whisk until yolks are broken down and combined into the whites. Then add remaining egg whites and cooled spinach mixture and whisk until combined. Pour into greased baking sheet.
Bake at 325 degrees for 18-22 minutes or until the tops of the eggs are no longer jiggly. Set aside to cool.
If using bacon, pre-heat the oven to 400 degrees. Arrange slices of bacon on a smaller baking sheet in a single layer.
Bake for 6 minutes, then rotate the pan in the oven so that the side that was in the front of the oven is now in the back. Continue baking for 8-10 minutes, then remove to a paper towel lined plate to cool. Pat off any excess grease.
*Note: ensure all components are completely cooled before assembling the sandwiches!
Slice the cooled eggs into 12 pieces and break bacon slices in half so they fit onto the sandwiches.
Place the english muffin bottoms on the counter (or onto a large baking sheet for easy cleanup). Add the cooled egg whites, then the cheese slices, then the meats. Add the muffin tops and tightly wrap the sandwiches in wax paper or foil. Freeze for up to 1 month.