The Malaysian roti bakar version of French toast is pan fried. The Hong Kong version is deep fried, and that one difference is worth about 135 calories of absorbed oil. Then it gets a butter slab on top (75) and syrup poured over (60). So a dish that starts as 160 calories of bread ends at 580, with 34g of fat. That is more fat than a baked pork chop rice serving of pork.
The peanut butter filling is not optional at most places and it is worth 90 calories per tablespoon. Some shops use kaya or condensed milk instead, which is similar. The thick-cut version, where each slice is nearly 3cm, absorbs a lot more oil. One Hong Kong dietitian ranking put the heavy peanut butter and butter version at around 850 calories, top of the cha chaan teng list alongside dry fried beef hor fun.
The context is what makes this bad. Nobody eats French toast as a meal. It comes at 3:30pm with a milk tea (110), after lunch and before dinner. That is a 690 calorie snack window. Do that three afternoons a week and it is over 2,000 calories, which is about a quarter kilo of body fat a week if nothing else in your day changes.