Spray 3 1/2- to 4-quart slow cooker with cooking spray. Layer half each of the potatoes, bell pepper and ham in slow cooker. Sprinkle with half of the onion.
In medium bowl, mix pasta sauce, milk and pepper; spoon half of mixture over ham. Layer with remaining potatoes, bell pepper, ham, onion and sauce (do not stir).
Cover; cook on Low heat setting 6 to 8 hours.
About 5 minutes before serving, stir mixture gently; sprinkle Parmesan cheese over top. Cover; cook on Low heat setting until cheese is melted. Top each serving with parsley.