Mix all of the ingredients in a bowl. Cover and marinate in the fridge for approx. 1 hr.
Cook the rice in salted water according to the packet instructions, drain. Remove the watermelon from the marinade (retain the remaining marinade), divide between two bowls. Arrange the remaining ingredients in a circle next to the watermelon, top with the tahini. Use the remainder of the marinade as a dressing and drizzle on top.