Thinly slice onion and add to bowl. Pour boiling water over top to cover and let stand about 10 minutes. Drain water, rinse with cold water and let sit on paper towels to absorb additional moisture.
Slice tomatoes into wedges. Add to medium size bowl.
Toss onions with tomatoes. Drizzle on 1-2 tbsp olive oil, salt and pepper and mix. Sprinkle on chopped herb and serve.