In a large bowl, mix together the spring onions, garlic, shallots and soy and fish sauces. Add the pork and stir to coat. Cover and put in the fridge to marinate overnight.
In a small saucepan, simmer the dressing ingredients together over a low heat until the sugar has dissolved. Leave to cool.
Preheat the grill to a medium-high heat.
Place the pork belly strips on to the grill pan and cook the pork for 3–4 minutes on each side, or until cooked through and slightly charred on both
sides. (Alternatively, you can cook this on a preheated barbecue.)
In a large bowl, toss together the cooked noodles, beansprouts, salad leaves, herbs and half the dressing.
Divide the noodle salad between four plates and place the pork on top. Drizzle over the remaining dressing and serve.