Preheat your oven to 375°F and lightly spray a 9×9 baking pan.
In a large bowl, combine ground beef, chopped onion, barbecue sauce, bread crumbs, beaten egg, chili powder, and salt.
Press the meat mixture evenly into the bottom of the baking pan. Bake uncovered for 20 minutes. Remove the pan from the oven and drain any excess grease.
In a separate bowl, prepare the instant mashed potatoes according to package instructions. Mix in evaporated milk, Monterey Jack cheese, crispy fried onions, butter, and cooked bacon.
Spread the potato mixture over the baked meatloaf. Sprinkle additional shredded cheese, bacon, and fried onions on top.
Place the casserole under the broiler, about 6 inches from the heat source, and broil for 3 minutes or until the top is golden and bubbly.
Serve your Cowboy Meatloaf and Potato Casserole with extra barbecue sauce, if desired.