Banh xeo looks like a light, vegetable heavy snack and it is really a fried pancake. The batter for one medium pancake is about 60g of rice flour and 40ml of coconut milk, 170 calories before it hits the pan. Then it hits the pan with a ladle of oil, because the crispness comes from shallow frying, and a medium pancake absorbs about 10g, 90 calories. That is 260 before the filling.
The filling is the healthy bit. Two or three prawns and a few slices of pork belly are about 70 calories for 40g, and the bean sprouts are 15. The published figure of 315 to 350 for a medium pancake with 11g fat, 40g carbs and 14g protein lines up with that. What changes it is size. A Hue or Da Nang banh xeo is palm size and 250; a Mekong style one is the size of the pan and 450 to 500.
Nobody eats one. The typical order at a banh xeo quan is two per person, with a plate of mustard greens and herbs and a bowl of sweet fish sauce, about 40 calories per bowl. Two medium pancakes plus sauce is 740. Two southern ones is 1,000. The greens are free and the pancake is meant to be wrapped in them, so at least the meal has volume.