1. Preheat oven to 170C fan-forced (190C Conventional).
2. Combine the tomato sauce and passata in a bowl and set aside.
3. Place a frying pan over medium heat. Add the olive oil and once hot,add the mince as one large patty,about 2cm thick. Use a spatula to press down on it and cook until charred and golden brown on one side,about 5 minutes.
4. Flip and cook the other side. While the second side is caramelising,add the onion around the edge of the pan so it can cook at the same time and absorb the juices. Cook until the onion is soft and translucent,and the meat is cooked mostly the way through – you still want some pink (about 5 minutes). Remove from the pan and set aside.
5. Return the frying pan to heat and add the gnocchi (you may need to add another ½ tablespoon of olive oil if you used lean mince). Cook,stirring often,until the gnocchi has taken on some colour on most sides,1–2 minutes. Turn off the heat.
6. Pour half the sauce into a baking dish. Drizzle over the mustard and arrange the burger cheese slices in a single layer,cutting to fit. Top with the onion and scatter with as many pickles as you can handle.
7. Use the spatula to break the meat patty into large bite-sized chunks. Place half the meat across the top – this is not a precise process,anywhere and everywhere is good. Add the gnocchi and top with the remaining sauce.
8. Push the remaining chunks of meat into the sauce and top with any cheese slice offcuts and the coarsely torn mozzarella.
9. Place in the oven uncovered for 30 minutes or until the top is bubbling and the cheese has melted. Taste a piece of gnocchi to ensure it has cooked through.
10. Season generously with salt and pepper. Scatter with chopped parsley,if using. Serve piping hot and with extra pickles.
*Note:A fresh,refrigerated gnocchi works best. Skip the boiling component and give it a flash fry in the pan to get some crispy edges,then straight into the baking dish. (If you were to use the supermarket aisle version,par boil them first or they may be too chewy.)