bring the vinegar to the boil in a small saucepan. Stir in the palm sugar until dissolved. Remove from the heat
stir in the papaya and set aside until the pickle has cooled completely.
For the pad Thai sauce
mix all of the ingredients together in a small bowl until combined into a smooth sauce.
For the noodles
discard any mussels with broken shells and any that refuse to close when tapped (if using). Heat a tablespoon of oil in a large
lidded wok and add the mussels. Cover with the lid and steam the mussels for 3–4 minutes
or until all of the mussels are opened. Discard any mussels that remain closed and remove the mussels from the remaining opened shells. Tip the noodles into a bowl and add the mussels.
Wipe the wok and add a tablespoon of oil. When hot
add the shallots and chillies and stir-fry for 1 minute. Add the squid rings and stir-fry for 1–2 minutes. Keep the wok on the heat
add the mussel and noodle mixture (or just the noodles if you aren't using mussels) and toss everything together. Pour in the pad Thai sauce and toss through the noodles until everything is coated and warmed through.
To serve
spoon the noodles into warmed bowls and garnish with the pickled papaya. Serve immediately with the lime wedges
