Preheat oven to 220°c/200°c fan-forced. Line a baking tray with baking paper. Place chicken on a tray and spray with a little oil. Cook for 10 minutes or until heated through.
Spoon sauce over the chicken, season, then scatter over mozzarella. Bake for 10 minutes or until cheese has melted. Top each chicken with a basil leaf, spray with a little oil, then bake for a further 5 minutes or until cheese is golden.
Spread bun bases with mayonnaise, then top with tomato, baby rocket leaves, and chicken. Sandwich with bun tops and serve.