Brown the sausage in a large skillet over medium heat, breaking it into crumbles, about 8-10 minutes. Drain and set aside to cool.
Grease a 9x13-inch baking dish and spread half the bread cubes on the bottom.
Layer the cooked sausage over the bread, then sprinkle with 1 cup of cheese. Top with remaining bread cubes.
In a large bowl, whisk together eggs, milk, mustard, salt, pepper, and garlic powder until well combined.
Pour the egg mixture evenly over the bread layers, pressing down gently to ensure all bread is soaked.
Top with remaining 1 cup of cheese, cover tightly with foil, and refrigerate overnight (or at least 4 hours).
In the morning, preheat oven to 350°F. Bake covered for 30 minutes, then uncover and bake for 15 more minutes until golden and set in the center. Let stand 5 minutes before serving.