Wash and dry the lettuce and herbs. Add the radishes and spring onions to a bowl with the vinegar, salt and sugar, then scrunch together with your hands, then set aside.
To make the dressing, crush the garlic and sugar to a paste using a pestle and mortar. Add the chilli and bash lightly to release some of its juices, then mix in the fish sauce and vinegar. Taste and adjust the seasoning if necessary: it should be sweet and salty, sour and spicy.
Cook the noodles in boiling water, according to the packet instructions, then drain and leave to cool.
To make the sausage patties, mash the garlic and sugar to a paste using a pestle and mortar, then add the fish sauce. Slit the sausages and squeeze the meat into a large bowl. Mix in the garlic paste, then form the mixture into 16 patties.
Grease a griddle pan with a little oil and put over a medium heat. When hot, cook the patties in batches for about 5 minutes on each side, or until really browned and crisp.
When you’re ready to eat, shred the lettuce. Divide the noodles between four large bowls, then top with the lettuce, some herbs, radish and sausage patties. Serve with the dressing for drizzling and extra herbs.