Preheat the oven to 200°C (fan-forced).
Heat the olive oil in a large, ovenproof frying pan over medium heat.
Add the onion and garlic and cook for 2–3 minutes until fragrant.
Add the zucchini, capsicum and mushrooms and cook for 5–7 minutes until the vegetables are softened.
Add the crushed tomatoes, passata and stock powder or cube, stir well.
Reduce the heat to low and simmer for 10 minutes.
Meanwhile, make the beef meatballs.
Combine the breadcrumbs and milk in a small bowl and set aside to allow the breadcrumbs to soak up the milk.
Combine the mince, egg, breadcrumbs/milk mixture, dried herbs, Worcestershire sauce, cheese and salt and pepper in a large bowl and mix until just combined.
Roll the mixture into small walnut-sized balls.
Add the gnocchi to the simmering sauce.
Stir through, then nestle in the meatballs.
Cover with the lid and bake for 25 minutes until the meatballs are just cooked.
Remove the pan from the oven, sprinkle the grated mozzarella and parmesan over the top, then dot with the buffalo mozzarella, if using.
Return, uncovered, to the oven for 10–15 minutes until the cheese is golden and bubbling.
Scatter on the basil and serve straight from the pan.
