Place fillets on a large piece of heavy-duty foil (about 18x12 in.), skin side down. Sprinkle with lemon zest, salt and pepper; top with white portion of green onions. Fold foil around fish, sealing tightly. Grill, covered, over medium-high heat until fish just begins to flake easily with a fork, 7-9 minutes., Meanwhile, place artichoke hearts, lemon juice and cheese in a food processor; process until smooth. To serve, open foil carefully to allow steam to escape. Remove salmon to serving plates, leaving skin on foil. Top fillets with artichoke mixture; sprinkle with remaining green onion.