Heat a large skillet over medium-high heat. Add sausage and cook, breaking it up with the back of a spoon, until lightly browned and crumbly, about 8 minutes. Add onion and bell pepper; cook until onion is softened, about 5 minutes. Blot any excess oil in the pan with a paper towel. Continue to cook until sausage is cooked completely, 5 to 7 more minutes. Remove from the heat.

Spray a slow cooker with cooking spray. Add sausage mixture, hash browns, and Cheddar cheese.

Whisk eggs, milk, salt, and pepper together in a bowl until well blended. Pour into the slow cooker and stir until evenly combined. Cook on Low 6 to 8 hours or on High for 3 to 4 hours, stirring after the first hour.