Creating the Overnight Croissant Breakfast Casserole is straightforward if you follow these simple steps:

1. Prepare the Dish: Grease a 9×13-inch baking dish with cooking spray or butter.
2. Tear the Croissants: Tear the croissants into bite-sized pieces and spread them evenly across the bottom of the baking dish.
3. Mix the Eggs: In a large bowl, whisk together the eggs, whole milk, salt, black pepper, garlic powder, and mustard until well combined.
4. Add Fillings: Stir in the cooked bacon or sausage, diced bell peppers, diced onion, and half of the shredded cheese into the egg mixture.
5. Combine Mixtures: Pour the egg mixture evenly over the croissant pieces, ensuring all pieces are soaked.
6. Top with Cheese: Sprinkle the remaining shredded cheese over the top of the casserole.
7. Chill: Cover the baking dish with plastic wrap and refrigerate for at least 8 hours or overnight.
8. Preheat Oven: In the morning, preheat your oven to 350°F (175°C).
9. Bake: Remove the plastic wrap and bake the casserole for 45-50 minutes, or until the center is set and the top is golden brown.
10. Cool and Serve: Allow the casserole to cool for a few minutes before slicing and serving.

By following these steps, you’ll create a breakfast casserole that is not only delicious but also a feast for the eyes!