Step 1Cut up the watermelon, remove the rind and seeds and chop the flesh into 1-inch cubes. (You'll need about 10 cups.)
Step 2Puree 1 cup of flesh to make juice. Add the paprika, ground red pepper, turmeric, coriander, garlic and salt to taste.
Step 3Heat the oil in a skillet over high heat and fry the cumin seeds 20 seconds. Immediately add the juice. Lower the heat and simmer until the liquid is reduced by one-third, about 5 minutes.
Step 4Add the lime juice and sugar to taste. Cook 1 minute. Add the watermelon pieces and cook over low heat 3 to 4 minutes, tossing to coat until heated through.