Wash, clean and slice the tomatoes. Peel the onions, cut into your strips. Serve alternately with tomatoes and season with salt and pepper.
Wash the mint and shake dry. Pluck the leaves off and roughly chop them, sprinkle over the lettuce. Shake the vinaigrette vigorously, spread over the salad and serve.
It is best to transport the vinaigrette separately for a picnic and drizzle over the salad before consumption.