Preheat oven to 350 degrees.
Spray the bottom and sides of the casserole dish with the cooking spray.
Lay four slices of the toasted bread in the bottom of the prepared casserole dish.
Top each slice of bread with two slices of American cheese.
Fry four eggs in the large skillet with the butter to over hard consistency.
Season each egg with salt and pepper to taste.
Place one egg on top of each toast and cheese slice in the casserole dish.
Top each egg sandwich with an additional two slices of American cheese, each sandwich.
Top each sandwich with a portion of the crumbled bacon.
Top each sandwich with the remaining toast slices.
In a large bowl, whisk together the remaining eggs, milk, salt, pepper and Dijon mustard until well combined.
Carefully pour the egg mixture evenly over the egg sandwiches in the casserole dish.
Bake in a preheated oven for 60 minutes or until the center of the casserole is set and no longer runny.
Remove the casserole from the oven and top evenly with the shredded cheddar cheese.
Return the casserole to the oven just long enough for the cheese to melt.
Remove the casserole from the oven and top with the chopped scallions.
Allow the casserole to sit for 15 minutes.
Slice, serve and enjoy!