Peel and dice the potatoes into evenly sized pieces, approximately 1-inch cubes for even cooking.
In a mixing bowl, combine the cheddar cheese, sour cream, cream of mushroom soup, milk, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
Add the diced potatoes to the crock pot. Pour the cheese mixture over the potatoes, ensuring all pieces are coated well.
If using, sprinkle the chopped green onions on top of the potato and cheese mixture.
Cover the crock pot with the lid and set it to cook on low for 4 hours, or until the potatoes are tender when pierced with a fork.
In the last 15 minutes of cooking, sprinkle the shredded mozzarella cheese over the top. Cover and allow it to melt before serving.
Once cooked, stir gently to combine the melted cheese and potatoes, and serve hot.