In a large bowl, combine the pre-cooked cornmeal and salt.
Gradually add the warm water, mixing with your hands until a smooth dough forms.
Let the dough rest for about 5 minutes to allow the cornmeal to absorb the water.
Divide the dough into 8 equal portions and roll each portion into a ball.
Flatten each ball into a disc about 1/2 inch (1.25 cm) thick.
Heat a tablespoon of vegetable oil in a large skillet or griddle over medium heat.
Place the arepas in the skillet and cook for about 5-7 minutes on each side, or until a golden crust forms.
Transfer the arepas to a baking sheet and place them in a preheated oven at 350°F (175°C) for about 10 minutes, or until they are cooked through and sound hollow when tapped.
In a large bowl, combine the shredded chicken, mashed avocados, mayonnaise, sour cream, finely chopped onion, lime juice, salt, and black pepper. Mix until well combined.
Remove the arepas from the oven and let them cool slightly.
Slice the arepas in half and fill each one with a generous portion of the chicken and avocado mixture.
Garnish with chopped fresh cilantro if desired.
Enjoy your meal!