Preheat your oven to 350°F. Line a baking pan with parchment paper and lightly coat it with cooking spray.
In a large bowl, whisk together the eggs, milk, and seasonings until well combined. Pour the mixture into the prepared baking pan.
Bake for 18-20 minutes, or until the eggs are just set. Keep a close eye on them during the last few minutes, as oven temperatures can vary and overbaked eggs can become rubbery.
While the eggs bake, cook your breakfast meat of choice and slice the cheese.
Let the baked eggs cool for about 5 minutes, then lift them out of the pan using the parchment paper. Cut the eggs into 16 equal squares.
Assemble the sandwiches by placing one egg square on the bottom, followed by your breakfast meat and a slice of cheese. Top with a second egg square to create the sandwich. Repeat until you've made all 8 sandwiches.
Wrap each sandwich individually in foil and store them in the refrigerator for up to 4 days. For longer storage, transfer them to the freezer.
When you're ready to enjoy one, unwrap the sandwich and microwave until heated through.