Preheat oven to 375°F (190°C). Grease a 10 x 15-inch rimmed baking sheet. Whisk eggs, milk, salt, and pepper, then pour into the pan. Bake 12 to 14 minutes until set and no longer jiggly.

Arrange bacon on a separate rimmed baking sheet and bake until crisp, 15 to 18 minutes, or cook in a skillet over medium heat. Drain on paper towels.

Cool the egg sheet 2 to 3 minutes, then cut into 6 even squares. If desired, toast the muffin halves. Assemble sandwiches with cheese, egg square, and bacon.

Let sandwiches cool completely, then wrap each tightly in parchment and then foil. Label and freeze up to 3 months.

To reheat, unwrap one frozen sandwich, wrap in a damp paper towel, and microwave on high 1 1/2 to 2 minutes until hot. Serve immediately.