Prepare the Batter: In a large bowl, whisk together rice flour, coconut milk, water, turmeric powder, and salt until smooth. Stir in chopped green onions. Let the batter rest for at least 30 minutes (or up to a few hours in the fridge).

Prepare the Filling: Heat oil in a large non-stick skillet over medium-high heat. Add sliced pork and cook until browned. Add shrimp and onion, cooking until shrimp turn pink and onion softens. Stir in bean sprouts, salt, and pepper; cook for 1-2 minutes until slightly tender-crisp. Remove from pan and set aside.

Make Nước Chấm: In a small bowl, combine fish sauce, sugar, lime juice, and warm water. Stir until sugar dissolves. Add minced garlic and chili (if using). Taste and adjust to your preference.

Cook the Crepes: Heat a non-stick pan (preferably 8-10 inch) over medium-high heat until hot. Add a small amount of oil (about 1 tsp) and swirl to coat. Pour about 1/2 cup of batter into the pan, tilting quickly to spread it into a thin, even layer.

Add Filling: Immediately place a spoonful of the prepared pork and shrimp mixture on one half of the crepe. Cover the pan and cook for 2-3 minutes until the crepe is crispy and the edges are golden brown.

Fold and Serve: Uncover the pan. Fold the crepe in half, pressing gently. Slide onto a serving platter. Repeat with remaining batter and filling. Serve immediately with fresh lettuce leaves, assorted herbs, and Nước Chấm for dipping.