Make a brine by mixing salt and water in a large saucepan and heating until the salt dissolves. Take off heat and set aside.
Cut up tomatoes and onions (into pieces about 2-3cm x 2-3cm). Place into saucepan with brine, cover and and leave overnight.
The next day, place the saucepan on the stove and heat until almost boiling. Take off the heat and strain off brine, retaining about a cup of it to mix with the dry ingredients.
Sift flour and spices together and then make a runny paste by adding some of the retained brine.
Place vinegar and sugar in a large saucepan and, when hot, add the flour and spice paste slowly, stirring to combine.
Add the vegetables. Bring to almost boiling point and take off heat immediately before boiling.