In a mixing bowl, combine masa harina and salt. Add the water and mix with the spoon until it thickens. Start kneading with your hands until a smooth dough forms. Let it rest for 5 minutes.

Divide the dough into 14 balls. With your hands form a pocket in the middle of the ball. Place one teaspoon of refried beans and one tablespoon of shredded cheese in the pupusa dough. Using the edges, cover the filling and form a ball once again. Flatten each filled ball into a thick disk shape.

Add oil to a non-stick pan and place over medium heat. Once hot, add the pupusa to the pan and cook for 3 minutes per side until it starts browning.