Fry onion in a small saucepan with sesame oil, stirring till it softens and becomes transparent. Make sure it doesn't brown. Add green capsicum and pineapple pieces. Stir for a minute. Add all the remaining ingredients and simmer over low heat, stirring constantly till the sauce thickens.

Use it as a base for other delicacies or store in an air-tight container in the refrigerator for upto 3 days.