Combine all batter ingredients except scallions in a large bowl for at least 3 hours, or overnight. Add scallions only right before making the crêpes.
Steam or soak mung beans in water until soft.
Boil pork until cooked through and soft, then slice thinly.
Wash bean sprouts and veggies.
Making Bánh Xèo - Each crêpe takes about 8-10 minutes
On medium-high heat add 1-2 teaspoons of oil and some onions
Immediately add a few pieces of pork and shrimp. Sauté, lightly mixing until very lightly browned and fragrant.
Pour in some batter and quickly tilt & rotate the pan so the batter is evenly spread. Add more batter if it wasn't enough to cover the pan. There should only be a thin layer of batter that almost flakes off at the pan edges where it's thinner. If your batter doesn't do that and is too thick, add a few tbsp water to the batter and mix to thin it out.
Lower the heat to medium. Add some mung beans, bean sprouts, and cover with a lid for about 3 minutes, or until bean sprouts are slightly cooked. The batter should also be slightly cooked and transparent around the edges. This step cooks the top side of the ingredients and batter while it steams since we won't be flipping the crepe.
Remove the lid, lower heat to medium-low and wait for the crêpe to become crisp. This takes about 5-7 minutes. This step lets the ingredients fully cook through, including the batter. It also lets steam escape so the batter can crisp up. Brush on a little oil around the edges if you're not seeing or hearing enough batter to pan contact. Fold in half, transfer to a plate and serve immediately. For batter troubleshooting please see the troubleshooting section in the post above.