Heat oil in a pan and saute the mushrooms, pinch of salt and pepper for a couple of minutes till it turns soft. Keep aside to cool.
Now wet your hands and take sufficient amount of the cooked rice in one hand. Make a hollow in the center and stuff little of the mushroom filling.
Cover it properly and press it carefully and gently to give it a triangle shape. Wrap it with a seaweed sheet. Sprinkle some sesame seeds and few finely cut seaweed and serve them just as it is as a snack or breakfast.