Banh cuon is one of the lightest things you can eat at a Hanoi breakfast stall, and the reason is water. The rice batter is steamed on cloth into sheets a millimetre thick, so a 200g plate of rolls is only about 220 calories even with the pork and wood ear filling. Compare that with 180g of xoi at 600. The filling is minced pork shoulder, maybe 30g per plate, so 60 of the 220 is meat.
The sides are where the plate goes up. Cha lua, the smooth boiled pork loaf, is 130 calories per 100g, so the two slices you get are about 60. Fried shallots are 25 for a teaspoon and most sellers are generous. The nuoc cham is warm, sweet and diluted, around 20 calories a bowl. Some stalls add a drop of ca cuong essence, which is just aroma. That is 300 for the standard plate.
The heavier orders are banh cuon trung, with a soft egg steamed inside the roll, and banh cuon with nem chua ran (fried fermented pork) or a fried banh tom on the side. Egg adds about 80 per roll. A plate with cha, egg and two fried nem is around 450 to 500. The published range of 200 to 600 per plate covers plain rolls at the bottom and minced pork with all the extras at the top.