Peel and grate mangoes, salt and leave for around 10 minutes. Squeeze out mango juice.
Cut onions and chilies in thin slices. Crush mustard seeds (not to fine) and stir turmeric in rice vinegar.
Heat oil in a pan and stir in onions, garlic-ginger paste, chili and mustard seeds till brown. Deglaze with turmeric-vinegar mixture, add mango and stir well. Add salt to taste.
Leave to cool. Fill in a jar and store in fridge.