Marinate the chicken: Cut the chicken thigh into bite-sized pieces. Add the chicken to a bowl with the sugar, salt, fish sauce, white pepper and cornstarch. Mix well until evenly coated. Set aside for at least 10 minutes while you prepare the remaining ingredients.
Prepare the prawns and noodles: Make sure the cooked egg noodles are separated and ready to stir-fry. Pat the defrosted prawns dry with kitchen paper.
Cook the chicken: Heat a wok over medium-high heat and add the vegetable oil. Once hot, add the marinated chicken and stir-fry for 3–4 minutes, until cooked through and lightly golden.
Fry the curry paste: Add the Thai red curry paste to the same wok and stir-fry for about 1 minute, until fragrant.
Add the coconut milk: Pour in the coconut milk and fish sauce. Stir well to combine with the curry paste.
Add the noodles: Add the cooked egg noodles and toss well, loosening the noodles as they cook so they become evenly coated in the curry sauce.
Add the vegetables and prawns: Add the sliced red bell pepper and stir-fry for 1 minute. Add the cooked chicken and prawns, then toss for another 1–2 minutes until the prawns are heated through.
Add the beansprouts and scallion: Stir in the beansprouts and scallion pieces. Cook for another 1–2 minutes, until the vegetables are just tender but still slightly crisp.
Serve: Divide the noodles between bowls and garnish generously with the crushed chopped peanuts. Serve immediately.