Julienne the potatoes. Slice the leeks, onions, pak choi, and red peppers. Finely chop the chilli, garlic, and ginger. Season the prawns with salt and pepper.
Bring a large pot of water to a boil. Add the potatoes and cook for about 8 minutes, until just cooked. Drain and set aside.
Heat a wok over medium heat. Add some sesame oil and fry the prawns with the chillis until crispy and cooked. Remove from the wok and set aside.
In the same wok, heat more sesame oil over medium-high heat. Add the ginger and garlic and sauté for about 1 minute until soft. Add the onions, red peppers, and leeks and stir-fry for 3-4 minutes. Add the boiled potatoes and mix carefully.
Add the soy sauce and lime juice, bring to a boil and remove from the heat. Place the prawns on top of the vegetables, cover the wok with a lid and leave to warm through.
To serve, sprinkle with cashew nuts and drizzle with sriracha.
