Step 1
To make the meatballs, combine the beef mince, onion, breadcrumbs, egg, olives and oregano in a large bowl. Season with salt and pepper. Mix until well combined. Roll tablespoonfuls of mixture into balls. Use your thumb to push an indent into 1 meatball and place 1 bocconcini half in the indent. Push the mince around the bocconcini to enclose. Transfer to a plate. Repeat with remaining meatballs and bocconcini. Place in the fridge for 30 mins to chill.
Step 2
Heat half the oil in a large non-stick frying pan over medium heat. Add half the meatballs. Cook, turning, for 5 mins or until brown all over. Transfer to a bowl. Repeat with remaining meatballs.
Step 3
Add the remaining oil to the pan. Add the onion, garlic and chilli. Cook, stirring, for 5 mins or until onion softens. Add the tomato. Cook, stirring, for 5 mins or until sauce boils and thickens slightly. Return the meatballs to the pan with the chopped basil and oregano. Cook for 5 mins or until heated through.
Step 4
Meanwhile, cook the spaghetti in a large saucepan of salted boilingwater following packet directions or until al dente. Drain well. Add to the tomato sauce and toss to combine.
Step 5
Divide the spaghetti and meatballs among serving bowls. Serve sprinkled with extra basil leaves and parmesan.