1Heat gas or charcoal grill. Cut 30x18-inch piece of heavy-duty foil. Place potato chunks on foil; sprinkle with salt. Cut butter into small pieces; sprinkle over potatoes. Sprinkle with cheese and bacon bits.
2Bring up 2 sides of foil over potatoes so edges meet. Seal edges, making tight 1/2-inch fold; fold again, allowing space for heat circulation and expansion. Fold other sides to seal. Pierce top of foil once or twice with fork to vent steam.
3Place foil packet, seam side up, on grill over medium heat. Cover grill; cook 45 to 60 minutes or until potatoes are tender. Carefully fold back foil. Sprinkle onions over potato mixture.