Cut tomatoes, onions, cabbage, cauliflower, and peppers into small pieces. Allow to stand in a brine, made by using quarter cup salt to each 1 litre water, overnight. Heat to boiling. Boil 15 minutes. Drain 1 hour. Combine mustard, sugar, and turmeric. Add to vinegar, which has been heated to boiling. Simmer, stirring constantly, until slightly thickened. Pour over vegetables. Stir until thoroughly blended. Heat to boiling.