Cut up watermelonand remove the seeds. Peel off the skin and chop the flesh in 11/2 inch cubes. Take one cup of the chopped watermelon and blend it to make a juice. To the juice add the chile or paprika, turmeric and coriander powders, garlic puree, and salt to taste.
Heat the oil in a wok and add the cumin seeds and within 20 seconds add the watermelon juice mixture. Lower the heat and simmer for 5 minutes so that the spices cook completelyand the liquid is reduced by a third. If using sugar, add it now, then add the lime juice and cook for a minute.
Add the remaining chopped watermelon and cook over low heat for 3 to 4 minutes, gently tossing it until all the pieces are covered in the spice mixture.