Peel the mangos, cut the flesh off the stone and dice. Clean the chilli, cut lengthwise, remove seeds, wash and finely chop. Clean and wash spring onions. Chop the white finely, cut the green into fine rings.
Heat the oil in a pot. Sauté the white of the spring onions, chilli and mustard in it. Add mango, sugar and vinegar. Bring to the boil and simmer for about 10 minutes. Mix in leek onion green, season with salt and pepper.