Heat the grill to high. Heat the oil in a non stick frying pan and cook for about 2 mins each side until golden.
Meanwhile mix cheese and tomatoes together. Take the chicken from the pan and wipe out the oil with kitchen paper. Return chicken to the pan and spread with the pesto and then pile the cheese and tomatoes on top.
Put under the hot grill until the cheese has melted. Serve with a green veg or salad.