Thinly slice the red onion and scatter over the tomatoes.
Combine all the ingredients for the dressing in a small bowl with a fork.
Drizzle over the salad. Serve immediately or chill until required.
If making in advance, remove from the refrigerator at least 30 minutes before serving to allow the salad to come up to room temperature.Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)