Mammoth basil leaves grow as large as your hand and are well suited for wrapping fish fillets or other quick-cooking foods for the grill. The leaves impart a delicate flavor to the fish and help keep the flesh moist while cooking. Soak the leaves in cold water to keep the basil from scorching on the grill. Experiment by substituting other scented basil leaves, such as lemon or cinnamon, for variations in flavor.
Light a charcoal fire in an outdoor grill and let it burn until the coals are covered with white ash. (Or preheat a gas grill on low heat.) While the fire is heating, soak the basil leaves in a bowl of cold water.
Cut the fillets vertically into 8 strips, each about 2 inches wide. Season the strips with the salt and pepper. Spread the pesto on the strips and top each with a lemon slice. Drain the basil leaves, shaking off most of the water. Wrap each strip in a wet basil leaf and secure with a toothpick or skewer.
Lightly oil the grill, place the fish on the grill, and cover. Cook until the fish is completely cooked in the center when cut with a sharp knife, about 10 minutes. Remove the leaves, and serve hot.