1Spray 5- to 6-quart slow cooker with cooking spray. In large microwavable bowl, microwave squash, onion and 1 tablespoon butter uncovered on High 10 minutes or until squash and onion are tender. Drain well.
2In slow cooker, mix squash mixture, 1 cup of the bread crumbs, 1/2 cup of the cheese, the sour cream, garlic salt, pepper and soup. In small bowl, mix remaining 1 cup bread crumbs, remaining 1/2 cup cheese and the melted butter. Sprinkle crumb mixture over squash.
3Cover; cook on Low heat setting 2 hours. Uncover; remove insert from slow cooker. Let stand 30 minutes before serving. Sprinkle with parsley.