Using a serrated knife, horizontally slice the top off the cobb loaf and set aside. Scoop out the middle of the loaf, leaving an edge of about 1cm so the shell isn’t too thin. Spread the mayonnaise around the base and sides of the loaf, and a little to the underside of the lid. Add a few slices of avocado, mash gently with a fork and season. Follow up with a layer of the pork, a few tbsps of the veg pickle, cucumber slices and a scattering of chilli and fresh herbs. Sprinkle over half the fish sauce. Repeat with the avocado (no need to mash this time), seasoning again, pork, pickle, cucumber, chilli and fresh herbs. Sprinkle over the remaining fish sauce. Replace the lid and wrap the entire loaf tightly. Transfer to the fridge and leave for a few hours, or overnight, before serving.