Heat the oven to 350°F and grease a 9x13 inch baking dish.
Cook the bacon in a skillet over medium heat until crisp, about 8 minutes. Move it to a paper towel, leave about 1 tablespoon of fat in the pan, then crumble the bacon.
Sauté the onion in the bacon fat until soft and lightly golden, about 5 minutes.
Spread the hash browns in the dish and press into an even layer.
Top with the onion, bacon, sausage, and half of the cheddar.
Whisk the eggs, milk, salt, pepper, garlic powder, and dry mustard until smooth, then pour evenly over the casserole.
Bake uncovered for 35 minutes. Sprinkle on the remaining cheese and bake 15 to 20 minutes more, until the center is set and the edges are golden.
Let it rest 10 minutes before cutting.
Serve with small bowls of Pace Picante sauce and sliced cherry tomatoes as optional toppings.