Season the prawns with soy sauce and white pepper and set aside.
Mix all the stir fry sauce in a small bowl and whisk until sugar dissolves.
Sautee the raw cashew nuts until crispy golden brown. Remove from the pan and set aside.
Stir fry the marinated prawns until charred and 80% cooked. Remove from heat and set aside.
Stir fry onion and dry chillies, then add garlic, ginger, and Sichuan peppercorns. Toss until fragrant, then add bell peppers.
Add the cooked prawns back to the wok, pour in the sauce. Once thick and glossy, turn off the heat and stir in cashew nuts and spring onions.
Transfer to a serving plate and serve immediately with rice or noodles.