Bring a large pan of water to the boil. Heat the oil in a large pan and cook the crumbled sausages for 5-8 minutes, until brown all over.
Add the crushed garlic and cook for 1 minute, then add the chopped tomatoes with a splash of water and season to taste. Simmer for 5 minutes.
Meanwhile, cook the gnocchi, then drain. Add the gnocchi to the sauce, then remove from the heat and stir through the rocket.
Transfer to a baking dish and sprinkle the mozzarella over the top, then place under a hot grill for a minute or two until the mozzarella is melted and golden.