Preheat oven to 350 degrees and spray a 9x13-inch baking dish with cooking spray.
Heat a large nonstick skillet over medium-high heat. Add sausage and break it apart with a wooden spoon. Add onion and bell pepper and cook until sausage is browned. Set aside.
Cut each biscuit into 4 pieces and scatter in the bottom of prepared baking dish.Scatter sausage mixture on top of biscuits.
Sprinkle cheese on top of sausage.
In a medium bowl, whisk together eggs, milk, salt, and pepper. Pour mixture evenly into the baking dish.
Bake for 35 to 45 minutes, or until eggs are set.
Notes
Use "Hot" sausage and add a pinch of crushed red pepper flakes if you want this casserole spicy.