Place the watermelon, sugar, and lime juice in a blender and process until liquefied.
Pour the mixture into a 9- by 13-inch baking dish and place dish in the freezer. Scrape with a fork every 30 to 45 minutes, loosening frozen bits from the sides and bottom with each stirring.
After the granita is completely frozen (3 to 5 hours), mix in chocolate chip “seeds.”