To prepare tuna: With a large chef's knife, chop tuna using quick, even, straight-up-and-down motions (do not rock the knife through the fish or it will turn mushy). Continue chopping, rotating the knife, until you have a mass of roughly 1/4-inch pieces.

Place the tuna, scallions, onion, ginger, 2 teaspoons fish sauce, soy sauce, brown sugar and pepper in a large mixing bowl. Gently combine, without overmixing, until evenly incorporated. Cover and refrigerate while you prepare the rest of the salad or up to 12 hours.

To prepare salad: Combine water, 3 tablespoons fish sauce, granulated sugar, vinegar, lime juice, ginger and garlic in a large bowl; stir until the sugar is dissolved. Reserve 1/2 cup of the dressing in a small bowl.

Bring a large saucepan of water to a boil. Add rice noodles and stir to separate well. Boil until soft but still resilient, 2 to 5 minutes or according to package directions. Drain and rinse the noodles under cold running water. Drain well, transfer to a medium bowl and toss with 2 tablespoons of the reserved dressing.

Add lettuce and bean sprouts to the dressing in the large bowl; toss to coat. Divide the mixture among 6 shallow serving bowls. Top with equal portions of the noodles.

Form the tuna mixture into 6 patties, about 3/4 inch thick. Coat a large nonstick skillet with cooking spray and place over medium heat (see Grilling & Broiling Variations). Add the patties and cook until firm to the touch, 2 to 3 minutes per side.

Place a tuna patty on top of each salad and drizzle each portion with some of the remaining dressing. Serve with a platter of carrots, cucumber, red onion and herbs and let diners choose their own garnishes. Grilling & Broiling Variations: Preheat grill to medium-high or preheat broiler. Oil the grill rack (see Tip) or coat a broiler pan with cooking spray. Cook patties until firm to the touch, 2 to 3 minutes per side.

Ingredient Note: Fish sauce is a pungent Southeast Asian condiment made from salted, fermented fish. Find it in the Asian section of large supermarkets and in Asian specialty markets. We use Thai Kitchen fish sauce, lower in sodium than other brands (1,190 mg per tablespoon), in our nutritional analyses.

Shopping Tip: Dried thin rice noodles (or rice sticks) are similar to mung bean threads, but they are a little thicker and are made with rice flour instead of mung bean starch. They're also called "bun" or "vermicelli-style" rice noodles. Look for them in the Asian section of well-stocked supermarkets or an Asian foods market.

Tip: To oil the grill rack, oil a folded paper towel, hold it with tongs and rub it over the rack. (Do not use cooking spray on a hot grill.) When grilling delicate foods like tofu and fish, it is helpful to spray the food with cooking spray.

MAKE AHEAD TIP: Cover and refrigerate the dressing (Step 4) for up to 1 week. Cover and refrigerate the tuna mixture (Steps 1-2) for up to 12 hours.