In a large bowl mix the diced mangoes with the grated ginger, seeds, chilli flakes and salt, then leave to rest for 15 minutes.
Heat the oil in a pan, then add the mango mixture. Cook for few minutes, then add the sugar and vinegar, mix and cook for 10 minutes on a low heat, stirring occasionally so the mangoes don’t stick to the pan.
After 10 minutes mash the mixture roughly, cover the pan and cook for another 10 minutes on a low heat. Take off the heat.
Pour the hot chutney into the warm, sterilised airtight jar(s). Enjoy with Indian food or simply a slice of toast.