PREHEAT oven to 450° F.
ARRANGE five 12 x 13-inch pieces of foil on work surface; coat lightly with nonstick cooking spray. Stir lemon peel into pesto. Divide asparagus and squash evenly down center of each foil sheet; spoon 1 tablespoon pesto mixture over vegetables. Place one fish fillet over pesto vegetables; sprinkle fish with salt and pepper. Spread each fish fillet with 1 tablespoon pesto mixture.
TOP each fish fillet evenly with tomato halves and green onion. Sprinkle with lemon juice. Bring up foil sides; double fold top and ends to seal each packet, leaving room for heat circulation inside. Place on 15 x 10-inch jelly-roll pan or rimmed baking sheet.
BAKE for 20 minutes or until fish is just opaque in center and vegetables are crisp-tender. Carefully open packets, allowing steam to escape away from you and let cool briefly. Using a spatula, gently push the fish and vegetables onto plate.
Cook's Tip: Fish Packets are also great on the grill! Preheat grill to medium. Place packets on grill; cover and cook over indirect heat for 20 minutes or until fish is opaque in center and vegetables are crisp tender. Remove from grill and open carefully.