Fry onions in oil until caramelised, stirring well to prevent burning. Add ginger and orange juice and cook until juice evaporates. Split vanilla bean down the middle and scrape out seeds with the back of a small knife, then add seeds and pod to the saucepan. Add pork and salt and gently cook 5 minutes, stirring well. Leave to cool in the saucepan, then stir in peanut butter and coriander.
Divide filling between the pastries, placing mounds of it in the centre of each one. Fold each one in half, gently pushing out any air and making sure the edges are sealed tightly by pressing with the back of a fork. Lightly brush with beaten egg and sprinkle with sesame seeds.