In a mixing bowl, combine the masa harina and salt.Gradually add warm water to the mixture, kneading it until you have a smooth, pliable dough.Divide the dough into 8 equal portions and roll each into a ball.
In another bowl, mix the shredded chicken, mozzarella cheese, refried beans, cumin, paprika, salt, and pepper. This mixture forms the flavorful filling for the pupusas.
Take one ball of dough and flatten it into a disc about 4-5 inches in diameter.Place a generous spoonful of the chicken filling in the center of the dough disc.Fold the edges of the dough over the filling, sealing it completely. Gently flatten the filled dough ball into a thick tortilla.
Preheat a griddle or a non-stick skillet over medium-high heat.Place the pupusas on the hot griddle and cook for about 3-4 minutes on each side, or until they develop a golden-brown crust.
While the pupusas are cooking, prepare the curtido by mixing the shredded cabbage, sliced onion, grated carrot, apple cider vinegar, water, dried oregano, red pepper flakes (if desired), salt, and pepper in a bowl. Allow it to marinate for a few minutes.
Serve the hot chicken pupusas with a side of curtido. The tangy crunch of the curtido complements the savory pupusas perfectly.