Place the onions with ice cubes and cover with water. Let the onions immersed for 10 minutes to reduce the bitterness.
Drain the onions transfer to a serving bowl. Add the watermelon cubes, lemon juice and zests, vinegar and season with salt. Mix it gently and keep in the fridge until serving.
Keyword lemon, red onion, salad, side dish, summer, vinaigrette, watermelon