At least two hours before, but better the night before, peel and finely chop the ginger into very thin batons. Place in a small bowl and add the lime juice (it should all be covered) then cover and place in the fridge to pickle. Place the yellow split peas in a separate bowl and cover with plenty water - set aside to soak.
Toast the chickpea flour in a small dry skillet/frying pan (ie no oil) over a medium heat. Stir as it toasts so that it cooks evenly. Take care as once it starts to brown, it progresses quickly. Once evenly light brown, remove from heat and tip the toasted flour onto a plate/dish to cool. This can be done ahead and stored at room temperature in a sealed container.
Peel and finely slice the garlic and prepare a plate with kitchen paper on top to drain after frying. Drain the soaked yellow split peas and dry off a little, as best you can, eg on kitchen paper (but separate from what you will use after frying).
Clean out the skillet/frying pan, warm over a medium-high heat and add oil to give an even layer. Once warm, add the garlic slices and fry until gently brown - watch closely as they quickly turn from brown to burnt. Once gently brown, use a slotted spoon to remove and drain and place on the kitchen paper to drain excess oil and crisp further.
If you like, use separate oil for frying the split peas, or simply add the yellow split peas after the garlic (in batches as needed - you don't want to cook too many at once as you want to be able to remove quickly once ready). Fry a few minutes until they are light golden then remove with a slotted spoon to prepared kitchen paper to drain. If the sesame seeds or peanuts are not toasted/roasted, fry them as well. All these fried elements can be made ahead and stored at room temperature in sealed containers. Save the garlic oil.
Once ready to assemble, shred the napa cabbage and thinly slice the tomato. Finely slice the pickled ginger. Chop the cilantro and mince the chili, if using.
Place the cabbage in a bowl and add all the other ingredients - the tomato, cilantro, ginger that you soaked in lime - save the lime juice, pickled ginger, sesame seeds, peanuts (slightly crushed if whole), chili, if using, and some fried split peas. Add around 3 tablespoon (45ml) toasted split peas for one recipe quantity (any extra make a tasty snack or can be used for another batch).
Add the fish sauce to the lime juice from pickling the ginger, and add 1 tablespoon (15ml) per recipe quantity of oil from frying the garlic. Drizzle this mixture over the salad, mix gently and serve.