Preheat your oven to 350 degrees. Spray a 9 by 13 inch baking dish with cooking spray and set aside.
Heat a heavy bottomed skillet over medium. Cook the bacon an the sausage together, breaking up the sausage. Stir frequently until both the bacon and the sausage are completely cooked through, about 12 to 15 minutes. Remove from the skillet and drain on a towel.
While the sausage and bacon are cooking, preheat a large non stick skillet over medium heat.
In a large bowl whisk together your eggs, milk, kosher salt, and pepper.
Spray your skillet with cooking spray and add the egg mixture. Allow to set for a moment, about 30 seconds and then using a spatula, start pulling the edge of the mixture towards to center of the pan. Continue to do this as the eggs begin to solidify. Once the eggs are light and fluffy (about 7 to 10 minutes), remove them from the heat.
Slice your slider rolls in half so that you have a bottom layer and a top layer. Place the bottom layer in the prepared casserole dish. (The tops might not all stay together, and that is okay. You will be able to arrange them at the end.)
Melt 4 tablespoons of butter. Whisk in 1/2 teaspoon garlic salt and 1/2 teaspoon ground mustard. Brush the bottom half of the rolls with the mixture.
Add the egg layer. Then add the bacon and sausage layer. Finally add the cheese.
Melt 4 tablespoons of butter. Whisk in 1/2 teaspoon garlic salt and 1/2 teaspoon ground mustard.
Add the tops of the rolls on top of the cheese. Brush with the remaining butter mixture. Cover the casserole dish with foil and bake for 20 minutes. Remove the foil and bake for 5 more minutes.