In a bowl, combine masa harina with salt. Add water and mix for 2 minutes. Let it rest for 15 minutes to hydrate the mix fully.
Coat your hands with oil. Form a small ball and with your thumb, create a well in the middle. Fill with cheese and pinch to close. Flatten the ball to create a small disk.
Add oil to the skillet and heat it over medium heat. Once hot, place the pupusas and cook for 4 minutes per side.
