Combine the ginger, shallots, garlic, 2 teaspoons of the turmeric, and fish sauce in a food processor and process until a coarse paste forms.
Put the fish in a bowl with the paste and pepper and stir to combine well. Cover the bowl with plastic wrap and refrigerate for 2–3 hours. Drain the fish well.
Making the Sauce
Combine all the ingredients in a bowl and stir to combine well, until the sugar has dissolved.
Put the rice-stick noodles in a large bowl, cover with boiling water and stand for 5 minutes. Drain. Bring a large saucepan of water to the boil, add the noodles and cook for 2–3 minutes or until tender – or cook according to the packet instructions. Drain well.
Combine the rice flour, remaining turmeric and salt in a bowl. Add the fish and toss well to coat, shaking off any excess.
Heat 2 tablespoons of the oil in a large heavy-based frying pan over high heat. Add the spring onion and onion and cook, tossing often, for 4–5 minutes or until the onions are lightly charred.
Now add half the dill, toss for 1 minute or until the dill has wilted then transfer to a bowl. Reduce the heat to medium and add the remaining oil to the pan.
Add the fish, in a single layer, and cook, turning once, for 5–6 minutes or until the fish is cooked through. Scatter over the onion mixture and the remaining dill.
Divide the noodles among warmed bowls and divide the fish mixture over the noodles. Scatter over the peanuts and extra spring onion, and serve with the sauce on the side.