Peel the cucumber, cut off the ends and cut the cucumber into thin slices. Wash the tomatoes, halve them if necessary and remove the stalk. Peel the onion and cut into fine rings.
For the dressing, mix the vinegar with lemon juice, mustard and rapeseed oil and season with salt, pepper and maple syrup.
Arrange the salad and drizzle with the dressing. Wash the cress, cut it off and spread it over the salad.