Lightly grease the inside of the Crockpot with the cooking spray.
Toss the sliced potatoes with salt.
Layer half the potatoes, onions, cubed ham, and shredded cheddar cheese in the slow cooker.
Repeat the layers with the remaining ingredients.
Combine the mushroom soup, milk, thyme, and pepper in a bowl.
Pour the mixture over the potatoes.
Cook the scalloped potatoes and ham for 3 to 4 hours on High or 6 to 8 hours on Low.
Top with chopped green onions before serving. Enjoy!