Preheat the oven to 375°F (190°C). Lightly coat a 9×13-inch casserole dish with nonstick cooking spray.

Wash and peel the russet potatoes. Cut them into evenly sized pieces and transfer them to a large pot.

Cover the potatoes with water and bring to a boil. Cook until the potatoes are tender and can easily be pierced with a fork.

Drain the potatoes thoroughly and return them to the warm pot.

Gently fold in the butter, cream cheese, sour cream, and milk until the potatoes are creamy while still retaining some texture.

Add the garlic powder, salt, black pepper, 1 1/2 cups of shredded cheddar cheese, and 1 cup of chopped turkey ham. Gently mix until evenly combined.

Transfer the potato mixture to the prepared casserole dish and spread it into an even layer.

Sprinkle the remaining 1/2 cup cheddar cheese and 1/2 cup turkey ham evenly over the top.

Bake the Loaded Baked Potato Casserole for 25–30 minutes, or until heated through and the cheese on top is completely melted.

Remove the casserole from the oven. Sprinkle with diced green onions and serve warm.