In a large jar with lid, dissolve the caster sugar in a little boiling water, add the salt, rice vinegar, carrot and daikon, stir it all around, making sure the vegetables are covered, pop the lid on, and refrigerate.
Make the sauce on the stove-top in a small saucepan over low heat by stirring the sugar, fish sauce, rice vinegar, and lime juice until the sugar has dissolved. Pour into a bowl and set aside to allow the flavours to meld together.
In a frying pan over medium-high, heat one tablespoon of oil until shimmering, fry the finely diced onion until soft, add the minced garlic, combine and fry for a minute until fragrant, then transfer to a small bowl and set aside to cool.
In a shallow dish, soak the slice of bread in enough water so it’s covered, then in a mixing bowl, combine the onion and garlic, ground pork, minced ginger, fish sauce, white pepper, sugar, soaked bread (excess water squeezed out), and finely chopped fresh herbs.
Roll a teaspoon of the pork mixture into a small meatball and microwave or fry until cooked to taste and, if needed, adjust the seasoning to suit your palate. Use a tablespoon to scoop out a heaped spoonful of pork mixture and roll it between your two hands a few times to roughly form a 5cm-diameter ball. Set it down on a tray and repeat. You should end up with around 16 meatballs.
In a wok or pan, heat three tablespoons of oil over medium heat under shimmering. Using tongs, transfer the meatballs to the pan so they’re not touching and shallow-fry, turning occasionally, until all sides are golden-brown, then transfer to a clean tray. You may have to fry them in two batches. Transfer the tray of meatballs, covered in foil, to a warm oven while you make the noodles.
Prepare the noodles by following the instructions on the packe: some call for boiling the noodles while others only require soaking. Transfer to a fine mesh strainer and allow to drain well.
Distribute the noodles between bowls; top with meatballs, spoon the sauce over them and sprinkle with crispy fried shallots; garnish with slices of cucumber and red chillies, the carrot and daikon quick pickle, and fresh herbs. Serve with wedges of limes, which add even more zing.