In a bowl, mix rice flour, cornstarch, and turmeric. Add 1 cup water (see notes) and the coconut milk, and whisk to blend. Stir in green onion.
Set a 12-inch nonstick frying pan (about 10 inches across bottom) over high heat. When pan is hot, add 1 teaspoon oil and tilt to coat bottom.
Stir rice flour batter to blend. Pour 1/2 cup batter into pan all at once and tilt pan to cover entire bottom evenly.
Distribute 1/3 of the bean sprouts and 1/3 of the shrimp evenly over half the crepe. Cook, uncovered, until crepe is browned and crisp on the bottom, 7 to 10 minutes. Fold plain side over filled side, then slide crepe onto an ovenproof plate. Keep warm in a 200° regular or convection oven up to 25 minutes. Repeat to cook 2 more crepes. Add seasoned fish sauce to taste