Cut Onion into fine slice. Take open flat pan, grease it with little oil.
Spread the sliced onion into the pan and sprinkle little sugar on the top. Keep the pan on medium heat and wait till the onions become golden brown. Let these caramelised onions get cool before using them.
Cut the watermelon into cubes, and de-seed it. Then make cavity in the top centre of the cube.Keep these cubes in the refrigerator.
In a bowl, take hung yogurt, Caramelised Onion, Lemon zest, Salt, Black Pepper and some chopped coriander.
Mix them well.
Take the watermelon cubes and fill the cavity with the yogurt mixture. Garnish with finely chopped coriander leaves.