In a medium bowl, using your hands, mix the masa harina with the water and ½ teaspoon salt until a soft dough forms. Cover the bowl with plastic wrap and let the dough stand for 30 minutes.
In a medium bowl, toss the chicken with the cheddar, queso fresco, and chorizo. Season with salt and cayenne.
Divide the dough into 8 pieces and roll each piece into a ball. Working with 1 ball at a time and keeping the rest covered, press the dough in the palm of your hand to form a cup with walls about ⅜-inch thick. Spoon 2 tablespoons of the chicken filling into the cup and pinch to seal. Pat the filled dough into a flat 3 ½-inch patty; pinch to seal any cracks. Set the pupusa on a baking sheet and cover with plastic wrap. Repeat with the remaining balls of dough and filling.
In a large nonstick skillet, heat ½ cup of the oil until shimmering. Add 4 pupusas and cook over high heat, turning once or twice, until golden and crisp outside and heated through, about 5 minutes. Repeat with the remaining pupusas, adding more oil to the skillet as needed. Serve the pupusas with sour cream, pickled jalapeños, chopped onion, guacamole, and hot sauce.
