Preheat the oven to 350°F. Coat a 13- x 9-inch baking pan with cooking spray.
Brown the sausage in a large skillet over medium-high heat for 6 minutes or until the sausage crumbles and is no longer pink. Remove the sausage from the skillet using a slotted spoon, reserving the drippings in the skillet.
Add the onion and bell pepper to the skillet and cook until softened, about 5 minutes. Stir in the spinach and cook for 1 more minute or until wilted. Set aside.
Process the cottage cheese in a food processor until very smooth. Add the eggs, salt, black pepper, and crushed red pepper and pulse until combined.
Arrange the sausage and vegetables in the bottom of the prepared baking dish along with the cheeses. Pour the egg mixture over the top.
Bake for 40 minutes or until the casserole is set. Let stand 5 minutes before cutting into wedges to serve.