Combine diced ham, diced potatoes, shredded cheddar cheese, cream of mushroom soup, and milk in a large bowl. Add garlic powder, salt, and pepper. Mix until well combined.

Spray slow cooker insert with non-stick spray. Transfer the mixture into the slow cooker evenly.

Cover and cook on low for 6-8 hours or high for 3-4 hours until potatoes are tender.

Stir gently before serving to combine ingredients evenly.

Garnish with chopped green onions just before serving.