Preheat the oven to 375 degrees F (190 degrees C).

Bring water and rice to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until rice is tender and water has been absorbed, 20 to 25 minutes.

Stir Colby-Jack cheese into the cooked rice; spread mixture over the bottom of a 9x13 glass baking dish.

Combine sausage, bacon, mushrooms, green bell pepper, and onion in a bowl. Pour over rice in the baking dish.

Beat eggs, milk, black pepper, and garlic powder together in a medium bowl. Pour evenly over the rice casserole. Top with Cheddar cheese.

Bake in the preheated oven until firm in the center, about 45 minutes. Remove from oven and let sit, 5 to 10 minutes.