Cut parchment paper into a 15-by-48-inch sheet. Fold in half and lay on half-sheet pan. Unfold and lay snapper diagonally on pan on top of 1 layer of parchment. Salt and pepper fish, inside and out. Place herbs inside cavity of fish along with 1/2 of the lemon and 1/2 of the red onion. Arrange couscous around the fish on all sides. Put garlic, and remaining lemon and red onion on fish and lay tomatoes and artichoke hearts around outside of couscous, creating a wall. Pour wine over fish and dot with butter. Fold over edges of parchment paper, stapling if necessary, to create an almost airtight seal. Bake for 30 minutes. Carefully open and serve (be aware of bones in the fish).