Heat a sauté pan, over a medium heat, drizzle a little olive oil.
Cook the meatballs and colour on all sides for 3-4 minutes, add the onion, carrot, garlic. Continue to cook for a further minute or so.
Add the tomato sauce, and chicken stock or water and simmer with a lid for 10 -15 minutes until the meat balls are fully cooked.
In the meantime, preheat the oven to 220˚C.
Place the sourdough slices on a baking tray. Drizzle with olive oil and sprinkle with half of the parmesan.
Transfer in the oven for 3-4 minutes to warm up and start crisp up. Remove from the oven.
In a small bowl, combine the ricotta, mozzarella, cheddar and parmesan. Season with salt and pepper.
Once the meatballs are cooked, divide the meatballs and sauce on the bread slices. Dot with cheese mixture. Place the tray back in the oven for 5 minutes to allow the cheese to melt and colour.
Remove from the oven, add a few salad leaves, and serve immediately.