Preheat your oven to 350°F (175°C).

In a mixing bowl, combine cooked chicken, mashed avocado, salt, and pepper.

Spread the mixture onto two slices of bread and top with cheese.

Cover with the remaining slices of bread.

Heat olive oil in a skillet over medium heat. Grill the sandwiches until golden brown on both sides and the cheese is melted.

Remove from heat, let cool for a few minutes, and then slice in half to serve.