Remove and discard the cabbage cores and finely shred the leaves. Slice the onion wafer-thin using a mandolin if you have one. Peel the mango and cut the flesh into matchsticks.
Put the mustard, vinegar and sugar in a bowl. Add the oil, salt, pepper and hot sauce, and whisk together. Toss in the cabbage, onion, mango and chillies and mix well.