Heat the oil in a frying pan. Add the meatballs and cook for 5 minutes until browned all over. Pour in the sauce and bring to the boil, then reduce the heat and simmer for 10 minutes. Taste and adjust the seasoning if necessary.
Lightly toast the ciabattas and split in half. Pile the meatballs and sauce on the bottom halves, top with the mozzarella and cook under a preheated hot grill for 1–2 minutes until starting to melt. Add some rocket, replace the ciabatta tops and serve immediately.