In a large mixing bowl, combine the masa flour and water.
Knead until a soft, pliable dough forms—like playdough.
If dry or cracking, add a little more water as needed.
Cover with a damp towel while you prepare the filling.
In a separate bowl, mix the shredded cheeses with the minced loroco.
Microwave the mixture for about 30 seconds if it's too firm.
Lightly moisten your hands with water and oil.
Scoop a ball of dough slightly larger than a golf ball and flatten it into a disc.
Spoon 1 - 2 tbsp of filling into the center.
Fold the edges over the filling to seal, then flatten into a disc about 1/4 inch thick.
Preheat a nonstick skillet or griddle over medium heat.
Cook the pupusas for 3 - 4 minutes per side until golden with melted cheese inside.
Transfer to a plate and wrap in foil to keep warm.
Repeat with the remaining dough and filling.
Serve hot with curtido and mild tomato salsa.
Enjoy!