Preheat your oven to 400 degrees Fahrenheit, and spray a 9×13 inch baking dish or casserole dish with non stick spray.
Place the breakfast sausage in a large skillet and cook sausage crumbling into small pieces, until sausage is cooked through.
Add bell peppers and onions to the skillet and cook a few minutes over medium heat more until the pepper is softened and the onion is translucent.
Drain the cooked sausage mixture, and add to a large mixing bowl.
Add hashbrowns and 1 ½ cups shredded cheese. Stir to combine.
Spread the sausage mixture into the prepared baking dish.
In another large bowl, whisk together the Bisquick mix, eggs, milk, salt and pepper and red pepper flakes. Pour the Bisquick mixture evenly over the casserole.
Sprinkle with remaining cheese, and bake uncovered for 45-50 minutes, until the center of the casserole is set, the top is golden brown and the cheese is melted.
Remove from the oven and allow to cool for about 10 minutes before cutting and serving.