Place the shiitake mushrooms in a heatproof bowl, cover with boiling water and allow to stand for 25 minutes or until the mushrooms are soft. Drain and reserve the liquid. Remove the stalks from the mushrooms and discard. Cut the caps into thin slices.
Trim the dry, woody ends from enoki mushrooms and separate the stalks. Toss the shiitake, enoki, oyster and button mushrooms with the choy sum and spring onions in a large bowl.
Gently separate the hokkien noodles and put in a large, heatproof bowl. Cover with boiling water and stand for 3 minutes, stirring occasionally to separate any noodles still clinging together. Drain well.
Place the garlic, sweet chilli sauce, soy sauce and reserved mushroom liquid in a small saucepan and simmer for 2-3 minutes, or until reduced and slightly thickened. Pour over mushroom mixture and toss to coat.
Add the warm noodles, cashews and sesame seeds to the mushroom mixture. Toss well to combine. Transfer to serving bowls.

These noodles are great served warm, but any leftovers can be refrigerated and eaten cold for a tasty lunch.