This is the dish that proves vegetables are not automatically low calorie. Morning glory is 20 calories per 100g raw. A plate of it should be nothing. But the fai daeng method needs a big splash of oil to catch fire, and the cook is not measuring. Fifteen grams is a conservative estimate; a generous stall can hit 25g, which puts the plate at 300. You are eating a salad that has been dipped in a deep fryer for 40 seconds.
The sauce is the other half. Oyster sauce is about 40 calories per tablespoon and mostly sugar, and tao jiew (fermented soybean paste) is salty enough that it makes you eat more rice. That is the real cost of this plate. It is 210 on its own, but it is a side dish, and it drags a 250 calorie plate of jasmine rice with it every time. Two spoons of the oily sauce over the rice adds another 60.
For the number, it is still the best vegetable order on most menus. Compare it to a fried omelette at 350 or a plate of fried tofu at 400 and the morning glory wins. Order it with the oil pulled back (mai sai nam man yer) and most stalls will do it. The plate drops to about 130 and nobody at the table notices.