Begin by preheating your oven to 375°F (190°C). Lightly grease your 9x13 inch baking dish with cooking spray or a small amount of butter to prevent sticking.
In a large mixing bowl, whisk together the 6 large eggs and 1 cup of milk until fully combined and slightly frothy. This mixture will create the custardy base that holds the casserole together.
Sprinkle in 1 teaspoon garlic powder, 1 teaspoon onion powder, 1/2 teaspoon salt, and 1/2 teaspoon black pepper into the egg mixture. Whisk again to evenly distribute the spices.
Fold in the 1 cup shredded cheddar cheese, 1 cup shredded mozzarella cheese, 1 cup diced bell peppers, and 1 cup diced cooked turkey bacon. Mix gently but thoroughly so every bite has a bit of everything.
Add the entire bag of frozen hash browns to the egg and cheese mixture. Stir well to coat the potatoes evenly with the custard and cheese.
Pour the mixture into your prepared baking dish, spreading it out evenly with a spatula. The casserole should be level and well-distributed.
Bake uncovered for 45-55 minutes, or until the top is golden brown and the casserole is fully set in the center. A toothpick inserted should come out clean.
Allow the casserole to cool for 5-10 minutes before slicing. This resting time helps it firm up and makes serving easier. Enjoy warm!