Whisk the fish sauce, water, lime juice, sugar, chiles, and garlic together in a bowl until the sugar dissolves. Divide the dressing among small individual dipping bowls and arrange the lettuce, basil, and cilantro on a serving platter.

Adjust an oven rack to the middle position and heat the oven to 200°F. Set a wire rack inside a rimmed baking sheet to keep the finished crêpes crisp.

Whisk the water, rice flour, coconut milk, scallions, salt, and turmeric together in a large bowl until the batter is smooth and well combined.

Heat a tablespoon of oil in a 10-inch nonstick skillet over medium-high heat until shimmering. Add the onion and salt and cook until the onion is softened and translucent, about 5 to 7 minutes.

Add the carrots to the skillet and cook until just tender, about 2 minutes. Transfer the onion and carrots to a bowl, let them cool slightly, and then stir in the bean sprouts.

Wipe out the skillet with paper towels and heat a teaspoon of oil over medium-high heat until it just begins to smoke. Stir the batter to recombine any settled flour, then pour a portion into the skillet while swirling the pan gently to distribute it evenly over the bottom.

Reduce the heat to medium and cook the crêpe until the edges pull away from the sides and the bottom is deep golden and crisp, 3 to 5 minutes.

Gently slide a spatula underneath the edge of the crêpe, grasp the edge with your fingertips, and flip it. Cook the second side until it is spotty brown, 2 to 3 minutes.

Slide the crêpe onto the prepared wire rack and place it in the oven to keep warm. Repeat the cooking process with the remaining oil and batter.

Divide the vegetable mixture among the crêpes and fold them in half. Serve immediately while warm, wrapping wedges of the crêpe in lettuce leaves with fresh herbs and dipping them into the sauce.