Simmer the beans in a small pan with the coconut milk, sugar, salt and 150ml (approximately 5 ounces) of water over low heat, stirring occasionally, until tender, about 30 minutes. When the liquid is almost evaporated, mash beans with a fork. Remove from heat and allow to cool. With a spoon, form balls about the size of a hazlenut, place them on wax paper and chill in the refrigerator.
For the dumpling dough, stir together 2 tablespoons of rice flour with 1/8 liter (approximately 1/2 cup) of water. Boil 1/4 liter (approximatley 1 cup) of water in a saucepan, remove from heat and stir in another 2 tablespoons of rice flour. Boil again while stirring in the remaining rice flour, until a smooth dough forms. Knead in a bowl with the vegetable oil for 10 minutes. Let rest.
Cut the ginger into slices and boil with sugar and 600 ml (approximatley 1 cup) of water at a low heat for 10 min until it begins to thicken.
Roll the dumpling dough into a to 4cm (approximately 1/2 inch) thick roll, then cut into 1/2cm (approximately 1/8 inch) thick slices. Place one ball of bean filling at the center of each disc, then close and pinch the tops. Bring salted water to a boil, then add the dumplings and reduce heat. Simmer for about 15 minutes.
Toast the sesame seeds in a frying pan, then remove and allow to cool. Strain the ginger syrup, pour into bowls over the dumplings, and serve sprinkled with sesame seeds.