Prepare the sauce by frying a clove of garlic in a little oil, then add the passata, basil and salt. Preheat the oven to 200°C. Bring a large pot of salted water to a boil. Add the gnocchi to the water following the package instructions, then drain.
Pour the gnocchi into a baking dish, add the sauce and grated Parmigiano Reggiano. Top with the diced mozzarella and some basil leaves.
Bake the gnocchi for 5-10 minutes, until cheese has melted. Remove from oven and serve hot.