Cook bacon until crispy over medium heat. Remove bacon and sautée onions in bacon fat until translucent, about 5 minutes.
In a greased oven-proof 9x13 baking dish, sprinkle bacon, onions, 1 cup of cheese, and hash browns.
In a large mixing bowl, mix together the Bisquick, milk, eggs, salt, and pepper and stir to combine. Pour mixture into the baking dish and bake for 40-45 minutes or until the mixture is cooked through.
Remove from the oven and sprinkle with the remaining cheese. Bake for another 3-4 minutes to melt the cheese. Garnish with scallions.