Place the tomato, sugar, cider vinegar, onions, mustard and seasoning in a large saucepan and bring to the boil over a moderate heat. Stir occasionally, making sure that the sugar has dissolved.
Boil for 25-30 minutes until thickened, then remove from the heat and allow to cool. Spoon into a sterilised glass jar and seal.
When ready to serve, toast the bread and cut into slices. Spoon the chutney into serving pots and serve with the toast slices.