Fill a pot half way with water. Put a steamer basket on top. Make sure the water does not come in contact with the steamer basket. Cover the pot and let it come to a boil.
Meanwhile, discard the water that was used to soak the sweet rice.
Put the soaked rice in a colander to remove any excess water from the rice.
Transfer the rice from the colander into a bowl and set it aside.
Pour the soaked mung beans in to a colander to discard the water and to remove any excess water.
Combine the soaked sweet rice and remaining mung beans in a large bowl. Mix well.
Add salt to the rice and mung bean mixture and mix well to combine.
Add this rice, mung bean mixture to the steamer basket.
Close the lid and leave it alone to steam for approximately one hour. After an hour, open the lid and check to see if the mung beans are soft. If they are, turn off the heat.
Add the vegetable oil to the cooked sweet rice and mung bean mixture. Mix well to combine.
And you've got yourself some delicious xôi vò.