Steam the yam until cooked. Mash the yam and add shortening, seasoning and wheat starch. Mix thoroughly until mixture becomes a paste and does not stick to your hands. Chill in the refrigerator for 30 minutes.
Remove yam paste and shape into a ring. Deep-fry the ring in hot oil until golden brown. Deep-fry the beehoon until crispy. Dish out and place on a large plate. Place the deep-fried yam ring over the crispy beehoon.
Heat oil and sesame oil in a wok, saute garlic until fragrant. Add the seasoned chicken and stir-fry well. Stir in mushrooms and the rest of the ingredients. Mix in combined seasoning.
Bring to a boil then simmer for one to two minutes until the gravy turns thick. Pour the mixed vegetables into the yam ring and serve the dish immediately.