Measure 2 cups of pre-cooked cornmeal into a bowl and add 1 tsp salt.
Pour 2 cups warm water gradually while stirring with a spoon to prevent lumps.
Mix until the dough is smooth, then add remaining water a little at a time to reach a soft, moist but not sticky texture.
Let the dough rest 4–5 minutes so the cornmeal hydrates fully.
Rub a little oil on your hands and divide the dough into 4 even portions (about 120 g each).
Shape each portion into a ball, then flatten gently into discs about 3–4 cm thick and 8–10 cm wide.
Heat a skillet or griddle over medium heat and brush lightly with oil.
Place arepas on the hot surface and cook 5–7 minutes per side until a golden brown crust forms.
If needed, lower heat and continue cooking 3–5 minutes per side to cook through; you can also finish in a 200°C (400°F) oven for 8–10 minutes.
Remove arepas and let them rest 2 minutes; slice partially open with a serrated knife to create a pocket and stuff with cheese, avocado or desired filling.