Heat the corn oil in a large soup pan on medium high heat. Once the oil is heated fry the onion until golden brown.
While the onions are cooking, place half of the beans and 1/2 cup of the reserved bean liquid in a blender and blend for 1 minute.
Once the onion is golden in color, about 4 minutes take the onion out with a slotted spoon.
Carefully stir the beans from the blender into the hot oil. Turn your heat down to medium low.
Next add the onion and the rest of the beans and reserved 1/2 cup cooking liquid into the blender and liquefy for a minute. Add the beans to the rest of the mixture that is already cooking.
Carefully stir the beans until no oil appears in the beans, about 3 minutes. Cook on medium stirring about every 5 minutes until the beans have darkened about 3 shades and are the consistency of refried beans in a can.
Place the shredded mozzarella, lorocco, and bell pepper in a food processor and process until the bell peppers and lorocco are chopped into tiny pieces and fully incorporated into the cheese.
Next, place the cheese mixture into a plastic bowl and warm the mix in the microwave for no more than 20 seconds.
Next -- and yes this sounds gross, squeeze the cheese mixture with your hands until it becomes like a soft putty consistency.
Set the cheese aside and get ready for the masa.
Place the masa mix and water in a bowl and stir until fully mixed. The masa should be very sticky but should form an easy ball when rolled. If not, add water until it is sticky but easy to work with.
Next, Place an egg size ball of masa in your hand (it helps to place a tiny bit of oil on your hands before doing this) and press the masa out in one hand to represent a small plate the size of your palm.
Place about a tablespoon of cheese down onto the masa, then a tsp of beans. Pull the sides of the masa up around the beans and cheese and roll it into a ball. Next, flatten it a tiny bit with your palms to form a thick disc. Pat the disc turning it between your hands about 6 times to flatten it more but to keep it in a round shape.
The pupusa should be a little less than 1/2 inch thick.
Place the pupusa on a large oiled non stick surface and cook on medium high until each side is golden brown, around 3 minutes on each side.