Combine the Chinese barbecue seasoning, 2 tsp fish sauce, 1 tsp sugar, 2 tsp oil and 2 tsp soy sauce in a large bowl. Cut the pork belly into 1cm-thick slices. Add the pork to the marinade and turn to coat. Set aside to marinate for 5-10 mins.
Step 2 — Prep salad ingredients
Meanwhile, finely chop the garlic, then using the flat side of the knife, mash to a paste (see cooking tip). Thinly slice the chilli, discarding the seeds if less heat is desired. Shred the carrot using a julienne peeler or cut into thin matchsticks. Thinly slice the radish using a sharp knife or mandoline. Pick the mint leaves, discarding the stems.
Step 3 — Make nuoc cham dressing
Bring a medium saucepan of water to the boil for the noodles. Put the garlic, chilli (if preferred, omit the chilli from the dressing and serve it at the table), remaining fish sauce, 2 tbs white vinegar, 1 tbs water and 2 tsp sugar in a bowl and stir to dissolve the sugar.
Step 4 — Cook pork belly
Heat a chargrill pan over high heat. Cook the pork, in batches, for 2-3 mins each side until charred and cooked through. Remove from the pan.
Step 5 — Cook noodles
While the pork is cooking, cook the noodles in the pan of boiling water for 7 mins or until tender. Drain, then rinse under cold water to prevent the noodles from sticking. Return the noodles to the pan.
Step 6 — Dress noodles and serve
Add half the dressing to the noodles and toss to coat. Divide the noodles, pork belly, salad leaves, carrot, radish and mint among bowls. Drizzle with the remaining dressing to serve.