To make the dressing, heat the oil in
a pan, then throw in the mustard seeds
and cook until they start to pop. Tip the
seeds into a bowl and allow to cool. Add
the rest of the dressing ingredients to the
bowl and whisk everything together.
Add the tomatoes, onions, cucumber
and radish to the dressing, stir to coat,
then allow to stand at room temperature
for 10 mins before serving.