Use a chef's knife and cutting board to dice the watermelon into 1/2-inch cubes, ensuring no large chunks remain.
Place the diced watermelon in a large mixing bowl and add the minced jalapeño, chopped cilantro, and salt.
4 cups watermelon, diced
Squeeze fresh lime juice over the mixture, then gently toss with a spoon until evenly combined and the ingredients are well coated.
4 cups watermelon, diced
Cover the bowl with plastic wrap and refrigerate for at least 10 minutes to allow flavors to meld.
Remove the salsa from the refrigerator, give it a gentle stir, and transfer to a serving bowl.
Garnish with additional cilantro if desired, and serve cold as a condiment or side.
4 cups watermelon, diced