How to Make It
In a small bowl, whisk all of the ingredients until the sugar dissolves.
In a medium bowl, whisk the rice flour with the turmeric and salt. Whisk in the water until smooth, then stir in 1/4 cup of the scallions.
Pour half the pancake batter into the skillet in an even layer and cook until browned on the bottom, about 4 minutes. Using a spatula, flip the pancake, then pour half the beaten egg evenly on top. Scatter 1/2 cup of the mung beans and 2 tablespoons each of the cilantro and scallions over the pancake and fold half the pancake over itself to form a half moon. Cook over moderately high heat, flipping once, until crisp on the outside and just cooked through, about 4 minutes longer. Transfer to a plate.
Cut the pancakes into wedges and serve with lettuce cups, mint leaves and the nuoc cham.