Add the sausage links, sliced peppers, sliced onions, and minced garlic to the slow cooker.
Pour the crushed tomatoes over the top. Sprinkle with oregano, salt, and black pepper.
Cover and cook on low for 6 to 7 hours until the sausage is cooked through and the vegetables are tender.
About 30 minutes before serving, bring the chicken broth to a boil in a saucepan.
Whisk in the polenta and reduce heat to low. Cook, stirring often, for 20 minutes until thick.
Stir the butter, milk, and Parmesan cheese into the polenta until smooth and creamy.
Slice the cooked sausage and spoon the peppers, onions, and sauce over bowls of polenta.