Preheat the oven to 375°F (190°C) and coat a 9x13 inch baking dish with cooking spray.
In a large skillet over medium-high heat, cook the breakfast sausage until browned and crumbled, about 8-10 minutes. Drain the excess fat and transfer the sausage to the prepared baking dish.
In the same skillet over medium-high heat, sauté the diced bell peppers and onion until tender, about 5-7 minutes. Add the vegetables to the baking dish with the sausage.
In a medium bowl, whisk together the eggs, heavy cream, salt, and black pepper. Pour the egg mixture over the sausage and vegetables in the baking dish. Sprinkle the shredded cheddar cheese evenly over the top.
Bake in the preheated oven for 25-30 minutes, or until the eggs are set and the cheese is melted and bubbly.
Allow the casserole to cool for a few minutes before slicing and serving.