Soak the shelled mung beans for at least 8 hours or overnight. Drain and rinse thoroughly.
Line a steamer basket with cheesecloth and steam the beans for 1 hour until soft.
Transfer the cooked mung beans to a food processor with ¼ cup (60ml) of water and blend until smooth.
Place the bean paste in a non-stick pan. Add the sugar and coconut oil, and cook over medium-low heat, stirring constantly, until thick.
Divide the mixture into 30g balls and refrigerate.
Make the water dough by combining flour, water, sugar, and oil. Knead lightly and let rest for 20 minutes.
Make the oil paste by mixing flour and oil to form a smooth paste.
Assemble the cakes by rolling out the dough, placing a ball of mung bean filling in the center, and sealing it.
Preheat the oven to 170°C (340°F). Arrange the cakes on a baking sheet and bake for 18 minutes, flip and bake for another 18-20 minutes.