Heat the olive oil in a large saucepan on a medium heat. Sauté the onion, garlic and ginger until soft.
Add the chilli flakes, cardamom, cumin, fennel and coriander seeds and cook for a further 4-5 minutes on a medium low heat.
Add the mango and cook for 3 more minutes, stirring to avoid the mixture sticking to the pan.
Add the vinegar and sugar, bring to a boil and reduce to a simmer. Simmer for 40 minutes until it becomes thick and syrupy