Combine the prawns with the marinade ingredients. Set aside.

Dry roast Sichuan peppercorns till fragrant then transfer them into a mortar and pestle to grind them to a fine powder. Set aside.

In a small bowl, combine the ingredients for the stir-fry sauce
Pour 1 tbsp vegetable oil into a large non-stick frying pan. Heat the pan over high heat. Coat the prawns in the flour, shake off any excess flour and then carefully place each prawn into the oil. Cook for about 2-3 minutes each side or golden brown. Drain on paper towel.

Discard the oil from the pan and clean it. Return it to medium-high heat. Add 1 tbsp of vegetable oil and then add the garlic, ginger and chillies. Saute until fragrant then sprinkle the ground Sichuan peppercorns. Mix through then add the stir-fry sauce and toss until well combined, thick and sticky.
Pour onto the prawn pieces. Scatter the spring onions and serve straight away.