Start by washing and dicing your potatoes, onions, and leftover cooked ham into bite-sized pieces. Aim for uniform sizes to ensure even cooking. Set aside your diced ingredients while you gather the rest of your supplies.

In a mixing bowl, combine the cream of mushroom soup and milk, whisking until smooth. This mixture will serve as the creamy base of your casserole.

In your slow cooker, start layering by placing half of the diced potatoes at the bottom. Follow with half of the diced ham, then sprinkle half of the diced onions and shredded cheddar cheese over the layers. Repeat this process with the remaining ingredients.

Pour the milk-soup mixture evenly over the layered casserole. Season the top with garlic powder, salt, black pepper, and paprika, gently mixing with a spoon if necessary to distribute the flavors consistently.

Cover your crockpot with its lid and set it to cook on low for approximately 6 hours, until the potatoes are fork-tender.

Once cooked, check the seasoning before serving. Adjust if needed and scoop generous portions into bowls.