Heat oil in a large frying pan over medium heat.
Add onions. Saute, stirring occasionally, for about 2-3 minutes or until soft. Make sure the onions don’t brown.
Add garlic and ginger. Saute, stirring, for about 30 seconds or until aromatic.
Add curry powder. Saute, stirring, for 30 seconds.
Add brown sugar. Stir to combine.
Add vinegar and water. Stir to combine. Simmer for about 2-3 minutes or until slightly thick.
Season with salt.
Add cayenne pepper and turmeric. Add mangoes. Stir to combine.
Cook, stirring occasionally, until the mangoes release juice and turn mushy. Add a little water if required.