Put the ciabatta rolls on a baking sheet and warm in a preheated oven, 180°C (350°F), Gas Mark 4, for about 10 minutes.
Meanwhile, thinly slice the mozzarella and slice the tomatoes. Halve, stone, peel and slice the avocados.
Remove the rolls from the oven and cut each roll in half. Layer the avocado, mozzarella and tomato slices on the 2 bottom halves, add the basil and sprinkle with pepper. Return the bottom halves with the filling to the oven for 2–3 minutes or until the mozzarella has melted. Put the top halves on top and serve immediately.