For the marinade, combine all the ingredients in a small bowl.
Place the minced pork and pork fat in a large mixing bowl and the pork belly in another bowl. Pour half the marinade over the pork mince and pork fat and the other half over the sliced pork belly and mix well to combine. Vigorously mix the pork mince to help bring the protein together. Scoop out the pork mince and then slap the mixture back into the bowl a few times to remove any air- this will help to prevent the mixture from falling apart when grilled. Cover and refrigerate the pork mince in and the sliced pork for at least 3 hours, or preferably overnight.
Meanwhile, for the pickles, combine the sugar and warm water in a bowl and stir until the sugar has dissolved, then add the vinegar. Place the green papaya and carrot in a bowl, pour over the pickling liquid and set aside for at least 2 hours, ensuring the ingredients are fully submerged.
Roll the minced pork mixture into golf ball-sized balls. If time permits you can then return to the refrigerator for 1-2 hours to firm up.
Preheat the charcoal grill. You can use a barbecue grill for this dish, but you won't achieve the same smoky flavour.
For the nuoc mam, warm the chicken broth in a small saucepan over medium heat. Place the warm water and sugar in a bowl and stir to dissolve the sugar. Stir in the fish sauce, vinegar, garlic and chilli.
When the charcoal is ready, slightly flatten the pork balls using the palms of your hands, then transfer to the grill. Carefully add the pork belly, being careful of the flare ups from the fat dripping onto the charcoal (which will make the meat black and bitter tasting). Cook the meatballs and pork belly, turning regularly, for 7-10 minutes or until cooked through.
To serve, place the cooked noodles and salad ingredients on a large serving platter. Drain the pickles and evenly divide amongst the small bowls. Add the meatballs and pork belly and evenly pour over the warm chicken broth and nuoc mam, finishing with a little pepper on top. Invite guests to dip a few noodles and herbs into their broth and eat, followed by mouthfuls of the meat and pickles.