Wash and dry potatoes. Cut potatoes in half, leaving the small ones whole, aiming to have all the potatoes about the same size. Lightly spray slow cooker with cooking spray, and add potatoes.
Stir in ranch dressing mix and olive oil, being sure to coat all the potatoes.
Cover, and cook on low 6 hours or on high 4 hours or until potatoes are fork tender, stirring once during cooking time.
When ready to serve, stir in chopped parsley.