Preheat oven to 375°F and grease an 8x8-inch baking dish.
In a medium bowl, combine cooked bacon, shredded cheese, onion, bell pepper, and mushrooms. Stir until all ingredients are well combined.
Pour mixture into the prepared baking dish and spread out in an even layer.
In a large bowl, whisk together eggs, garlic powder, black pepper, salt, and milk until blended. Pour egg mixture over the bacon and cheese layer in the baking dish.
Bake in preheated oven for 30-35 minutes or until the top is golden brown and the center is set.
Remove from oven and let cool for 10 minutes before serving.
Interesting Facts
This casserole can be made ahead of time and stored in the refrigerator until you are ready to bake it.
You can use any type of cheese you like in this dish, from mozzarella to pepper jack.
You can add other vegetables or meats to this dish to customize it to your tastes.