Place the Italian sausage links in the bottom of the slow cooker. Add the sliced red bell peppers, onion, and minced garlic on top.
Pour the crushed tomatoes over the vegetables and sausages. Sprinkle with dried oregano, salt, and black pepper.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the sausages are fully cooked and the peppers are soft.
About 30 minutes before serving, bring the chicken broth and milk to a simmer in a medium saucepan over medium heat.
Slowly whisk in the polenta. Reduce heat to low and cook, stirring often, for 20 to 25 minutes until thick and creamy.
Stir the butter and Parmesan cheese into the polenta until melted and smooth.
Slice the cooked sausages and serve them with the peppers and sauce over the polenta. Sprinkle with chopped fresh parsley.