Marinade the fish in soy sauce and cornstarch while preparing others. Microwave the hor fun noodles for about 1 minute and then separate and loosen the noodles
Preheat your wok/pan (that can resist high heating) on high heat. Add 2 Tbsp of oil. Add half of the garlic and stir fry for about 5 seconds. Add hor fun and stir fry them until they are slightly charred on some spots. Dish out and set aside
Prepare fish and bean sprouts:
Wipe the wok/pan clean. Bring it back to hot. Add 2 Tbsp cooking oil. Add green onion stalks, another half of garlic and stir fry for about 10 seconds. Add bean sprouts and stir fry for another 5 seconds. Add fish slices and stir fry for about 1 minute or until the fish slices are cooked through. Dish out and scattered on top of the hor fun you prepared earlier
Prepare gravy:
Pour chicken stock into the same pan. Bring to a boil and then season with soy sauce, a pinch of sugar, pepper, and salt to your taste. Stir in the tapioca flour mixture and cook until the sauce is thickened. Pour this over hor fun and sliced fish mixture and serve immediately
Notes
I cannot find snakehead fish where I am and so I substituted with flounder fillet