Make the dressing first, so that all the flavours have time to mingle. In a large bowl or measuring jug, dissolve the sugar in 50ml of boiling water.
Remove and discard the tough outer layers of the lemongrass and finely chop. Stir through all the other ingredients and squeeze in the lime juice, then set aside.
Peel and thinly slice the onion. Heat a little sesame oil in a frying pan and fry the onion over a low-medium heat, until soft and golden at the edges, about 10 minutes. Set aside.
Drain the tofu and break into very rough chunks. In the same pan, heat 2 tablespoons of the sesame oil over a medium heat, then add the tofu and fry until it starts to go crispy on the edges – about 5 minutes.
Stir in the hoisin sauce and keep it on the heat for about 3 minutes, until it’s sweet and sticky and coats all the tofu. Add the sesame seeds for the final minute, then it’s done.
Soak the noodles in boiling water until soft, then drain.
For the salad, grate the carrot and cucumber (or use a crinkle cutter). Finely slice the baby gem and spring onions. Pick the mint leaves. Combine all the salad ingredients in a bowl and set aside.
Crush the peanuts, finely slice the chilli and cut the lime into wedges.
To assemble your meal, divide the noodles between serving bowls, followed by the salad, then the tofu and onion, scatter over the peanuts and chilli and generously share out the dressing. Serve with extra toasted sesame oil, lime wedges and chilli sauce.