Grease or line the bottom of the slow cooker. Add the defrosted hash brown potatoes, sliced kielbasa, diced onion, diced bell pepper, and half of the shredded cheddar cheese to the greased crock pot.
In a separate bowl, mix together the cream of mushroom soup, milk, garlic powder, black pepper, and salt.
Pour the soup mixture into the slow cooker and stir everything together to evenly coat the potatoes and kielbasa mixture in liquid. Top with the remaining cheese.
Cover the slow cooker and cook on HIGH for 3 hours, on LOW for 5 hours, or until the potatoes are tender and the casserole is hot and bubbly.
Stir the casserole well. Garnish with sliced green onions (optional). Serve hot and enjoy!
Notes
Storage
Refrigerate: You can store the casserole in an airtight container in the refrigerator for 3-4 days. Let the casserole cool down to room temperature before storing it in the fridge. When reheating, you can use a microwave or oven until the internal temperature reaches 165°F (74°C).
Freeze: Let the casserole cool down to room temperature and then transfer it to a freezer-safe container or freezer bag. Frozen casseroles can last up to 3 months in the freezer. To reheat the frozen casserole, thaw it overnight in the fridge and then reheat it in the oven or microwave until it reaches an internal temperature of 165°F (74°C).