Crisp Hoi An Pancakes

Whisk flour, turmeric, salt, and 1 1/2 cups water in a large bowl until smooth. Cover and let sit at room temperature 1 hour (this allows the rice flour to hydrate; the batter will get creamier as it sits).
Heat 1 tablespoon oil in a medium nonstick skillet over medium-high heat. Add shrimp, season with salt and pepper, and cook, tossing often, until cooked through, about 3 minutes. Transfer to a plate.
Wipe out skillet and return to medium high heat. Add remaining 4 tablespoons oil. Mix batter to reincorporate rice flour, pour 1/2-cupful into skillet, and swirl pan to evenly spread out batter. (Be careful: Batter will splatter.) Cook pancake, shaking pan occasionally, until almost cooked and edges begin to curl, about 4 minutes. Top with one-fourth of scallions, one-fourth of bean sprouts, and one-fourth of shrimp and cook until pancake is golden brown and crisp, about 1 minute. Using a spatula, fold pancake in half, forming a half-moon. Transfer to paper towels to drain. Repeat with remaining batter (mixing before adding to pan), scallions, bean sprouts, and shrimp to make 3 more pancakes, adding more oil to skillet as needed.
Cut pancakes into wedges. To eat, tuck each wedge inside a lettuce leaf along with some herbs and dip in Nuoc Cham.