In a large mixing bowl, combine masa harina, warm water, and salt. Mix until a soft dough forms. If the dough is too dry, add water 1 tablespoon at a time until pliable.
Divide the dough into 6 equal portions and roll each into a ball.
Flatten each ball into a thick disc about 3 to 4 inches in diameter and 1/2 inch thick.
Pinch the edges of each disc to create a raised border around the perimeter to hold toppings.
Heat about 1/4 inch of vegetable oil in a large skillet over medium heat.
Fry each sope for 2 to 3 minutes on each side or until golden and cooked through. Remove and drain on paper towels.
In a small skillet, heat 1 tablespoon vegetable oil over medium heat. Add chopped onion and minced garlic; sauté for 2 minutes until softened.
Add shredded chicken, ground cumin, chili powder, and black pepper. Stir to combine and cook for 3 to 4 minutes until heated through and fragrant. Remove from heat.
Spread about 2 tablespoons of refried beans evenly on each fried sope.
Top each sope with a generous portion of the seasoned shredded chicken mixture.
Add shredded lettuce and diced tomato on top of the chicken.
Drizzle sour cream over the toppings and sprinkle crumbled queso fresco.
Garnish with fresh cilantro leaves.
Serve immediately while warm.