To remove the bitter taste of onions, add the thinly sliced onions to a bowl of COLD water for 10 minutes and then drain.
In a blender, add lemon juice, olive oil, mint leaves, salt, black pepper and pomegranate molasses. Blend to form the vinaigrette.
In a large bowl, combine watermelon, cucumbers and the red onions.
Pour the vinaigrette over it.
Add the chopped walnuts, stir and serve!