Preparation Place salmon fillets, 3 tablespoons tartar sauce, 1 tablespoon dill, salt, and pepper in processor. Blend using on/off turns until coarsely ground. Form into two 1/2-inch-thick patties. (Can be made 6 hours ahead. Cover and refrigerate.) Prepare barbecue (medium-high heat). Whisk 1/2 cup tartar sauce, 1 tablespoon dill, and lemon peel in medium bowl to blend. Grill rolls until toasted. Transfer to 2 plates and spread bottom halves generously with sauce. Grill patties until fish is cooked through, about 2 minutes per side. Place burgers atop sauce on rolls. Top each with onion slices, 2 lettuce leaves, and top half of roll. Serve, passing remaining sauce separately.
Preparation Place salmon fillets, 3 tablespoons tartar sauce, 1 tablespoon dill, salt, and pepper in processor. Blend using on/off turns until coarsely ground. Form into two 1/2-inch-thick patties. (Can be made 6 hours ahead. Cover and refrigerate.) Prepare barbecue (medium-high heat). Whisk 1/2 cup tartar sauce, 1 tablespoon dill, and lemon peel in medium bowl to blend. Grill rolls until toasted. Transfer to 2 plates and spread bottom halves generously with sauce. Grill patties until fish is cooked through, about 2 minutes per side. Place burgers atop sauce on rolls. Top each with onion slices, 2 lettuce leaves, and top half of roll. Serve, passing remaining sauce separately.