In a large frying pan heat the chorizo over a medium heat for 5 minutes. This should render out the lovely red oil from the sausage.
Remove the chorizo and set aside in a bowl, leaving the oil in the frying pan.
With the frying pan back over a medium heat add the garlic and fry for a minute before adding in the onions. Stir the onions and garlic to coat with the chorizo oil and cook for a few minutes until the onions begin to soften.
Slowly add the vegetable stock, stirring as you do so. Reduce heat and simmer for 10 minutes to reduce the liquid down.
Add in the chopped tomatoes and allow to heat through for a couple of minutes before adding back the chorizo. Stir thoroughly.
While the sauce is simmering cook your gnocchi according to the packet instructions.
Before draining the gnocchi, retain some of the cooking water.
Once your gnocchi has been drained, return it to the pan and pour over the sauce and stir well. If you're using the mozzarella cubes add them now and stir until melted (return to the heat to help this along if you like). If you prefer a thinner sauce you can now add back some of the cooking water from the gnocchi to loosen it.
Just before serving stir in the chopped basil leaves (retain some for garnish) and salt and pepper to taste.
Serve with freshly made garlic bread