In a medium bowl, combine the warm water and kosher salt. Gradually stir in the precooked white cornmeal until no dry patches remain. Let the dough rest for 5 minutes so the cornmeal can hydrate.

Knead the dough briefly with clean hands until smooth and soft. It should feel moist and hold together when squeezed. If it cracks badly, knead in water 1 teaspoon (5 ml) at a time. If it is sticky, work in a little more cornmeal.

Divide the dough into 4 equal portions. Roll each into a ball, then gently flatten into a disk about 4 inches (10 cm) wide and 3/4 inch (2 cm) thick. Smooth any cracks around the edges with damp fingers.

Heat the oil in a large nonstick or cast-iron skillet over medium heat. Add the arepas and cook until golden brown and lightly crisp, about 6 to 8 minutes per side. Reduce the heat if they brown too quickly before warming through.

Transfer the cooked arepas to a cutting board and let them rest for 2 to 3 minutes. Meanwhile, toss the avocado slices with lime juice and fine salt.

Using a small serrated knife, carefully split each warm arepa around the edge to create a pocket, leaving one side attached if desired. Fill each arepa with queso fresco and avocado. Serve warm.