To make mung bean hopia, start with the filling before moving on to the dough and assembling them. To make the filling, soak 14 ounces of dried, peeled split yellow mung beans in water for four hours, then drain them.
Move the beans into a saucepan, and add water 1/8 inch above the beans before bringing it to a boil. Once the beans start to soften, turn the temperature down to medium, and scoop out any foamy water. Continue cooking and stirring the beans until they turn into a paste, then mash the paste with a wooden spoon. Move the paste to a food processor, and gradually add 1 cup of sugar and 1/2 teaspoon of salt. Move the paste onto a microwave safe dish, and microwave it for five minutes or until it has dried out enough that it can be shaped into a ball.
To make the first dough, add 1 cup of flour into a bowl, and form a well. Pour 1/4 cup of grapeseed oil or 1/4 cup of canola oil into the center of the well, then mix it with a fork until loose, coarse crumbs form. To make the second dough, create a well with 2 cups of flour, but whisk 3/8 cup of oil together with 3/8 cup of water before pouring it in the center of the well. Stir it until if forms dough, and divide the dough. Finally, to assemble the hopia, brush the tops with beaten eggs, and bake for 20 minutes at 375 degrees Fahrenheit.