For the noodle dough, combine the flour mix, xanthan gum, salt in a bowl.
Add the water and oil and use a fork to bring it all together then use your hand to knead the dough for 4 minutes. Use more water if needed to make it smoother.
Wrap in a damp cloth and let it rest on the bench for 10 minutes.
Using more flour mix, roll the dough on a floured bench with a rolling pin until 3mm thick rectangle. Flour this and then gently roll up and slice the noddles approx. 5mm wide. Gently transfer them to a plate.
Bring a pot of water to the boil and add a good pinch of salt.
Mix the miso sauce ingredients together and set aside.
Place the baby spinach into a colander over the sink.
Cook the noodles in the boiling water for 2 minutes then drain through the baby spinach in the colander and give a quick rinse with water to cool. Slightly.
Onto a large shallow and wide bowl, pour the miso dressing and add the prepared shallots, garlic, ginger and cucumber and coriander if using.
Add the slightly warm noodles and toss everything to combine.
Serve straight away with the tahini drizzled if desired.