Step 1
Use a large serrated bread knife to cut the baguettes in half horizontally, not cutting all the way through. Scoop out the bread on the inside of the rolls, leaving a 1cm border. Process the bread in a food processor until fine crumbs form.
Step 2
Place the mince, onion, garlic, oregano, egg and 1/2 cup of the breadcrumbs in a bowl. Season. Mix gently with your hands until well combined. Using wet or oiled hands to stop the mince from sticking, roll heaped tablespoonfuls of the mince mixture into 16 meatballs.
Step 3
Heat the oil in a large frying pan over medium-high heat. Add half the meatballs and cook, turning, for 5 minutes or until golden. Transfer to a plate. Repeat with the remaining meatballs. Wipe the pan clean.
Step 4
Preheat the oven to 200C/180C fan forced. Heat the passata in the frying pan over medium heat until it comes to a gentle simmer. Add the meatballs and cook, turning, for 8-10 minutes or until cooked through and the sauce thickens to coat the meatballs.
Step 5
Place the meatballs in the baguettes, alternating with bocconcini. Drizzle over a little extra sauce from the pan. Sandwich the baguette halves back together to shut, and place on a baking tray. Bake for 5-8 minutes or until warmed through and the cheese melts slightly. Open the rolls slightly and top with basil just before serving.