1Heat coals or gas grill for direct heat. Spray 13x9-inch aluminum foil pan with cooking spray. Rinse spinach; shake off excess water, but do not dry. Place about three-fourths of the spinach leaves in pan, covering bottom completely.
2Mix poultry seasoning, chili powder and salt. Lightly rub into both sides of fish. Place fish on spinach, folding thin tail ends under and, if necessary, overlapping thin edges slightly. Drizzle with butter. Cover fish completely with remaining spinach.
3Cover and grill fish and spinach 4 inches from medium heat 8 to 10 minutes or until fish flakes easily with fork. Check after about 3 minutes; if top layer of spinach is charring, sprinkle with about 1/4 cup water. Serve fish and spinach from pan with a slotted spoon. Serve with lemon wedges.