1.Soak tamarind pulp in water for 30 minutes. Pour tamarind into a fine strainer over a small bowl; push as much pulp through the strainer as possible, scraping underside of strainer occasionally. Discard any tamarind solids left in strainer and reserve pulp liquid in bowl.
2.Heat oil in wok; stir-fry ginger, garlic and chilli until fragrant. Add duck and capsicum; stir-fry until capsicum is tender and duck is heated through.
3.Add stock to wok with sauces, sugar and reserved pulp liquid, bring to a boil. Boil 1 minute. Add bok choy and stir-fry until just wilted. Add snow peas and onion, and stir-fry until both are just tender. Remove wok from heat. Toss coriander leaves through stir-fry.