Combine the cold stock, sugar, lime juice, black vinegar, salt, mushroom seasoning powder and lime zest in a bowl with some space left for adding noodles and cabbage. Give it a stir, add the herbs, and pop the bowl back in the fridge for 20-30 minutes.
Meanwhile, cook the rice noodles per packet instructions and strain. Dump them into some cold water to stop the cooking, strain again, and plop them on a dish alongside the shredded cabbage.
Remove the stock from the fridge, give it another stir, add the peanuts, fresh chillies, and toasted chilli powder. Serve with the cooled noodles and cabbage.