1Heat gas or charcoal grill. Cut 18x18-inch sheet of heavy-duty foil. Break off tough ends of asparagus as far down as stalks snap easily. Place asparagus on center of foil. Top with butter, salt and pepper.
2Bring up 2 sides of foil over asparagus 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.
3Place packet on grill over low heat. Cover grill; cook 10 to 15 minutes, rotating packet 1/2 turn after 4 minutes, until asparagus is tender.
4To serve, cut large X across top of packet; carefully fold back foil to allow steam to escape. Sprinkle with cashews.