Mix salt, sugar, pepper, mustard and vinegar thoroughly. Pour in the oil and mix.
Tomatoes and persimmons cut in half, and then cut into thin slices. Cut the onion into half rings.
Put the vegetables in a deep bowl, pour over the dressing, mix gently. Leave to soak for at least 30 minutes.
With a slotted spoon, carefully transfer the salad to a dish, lightly pour 1-2 tablespoons of dressing, sprinkle with pomegranate seeds.