Place watermelon, jalapenos, cilantro, lime juice and onion in a medium bowl; stir well to combine. Season with salt. Serve at room temperature or chilled.

Tip: Melon selection & storage: Look for symmetrical unblemished melons, without flat sides, that have a creamy yellow spot on the bottom indicating ripeness. At 92% water, this fruit should feel heavy when you heft it. Precut melon flesh should be dense, firm and appear moist. Store in the refrigerator for up to a week or keep in a cool, dark spot. Cover the cut surface of melon with plastic wrap and refrigerate.

Ingredient Note: The seeds and surrounding membrane are the spiciest part of the chile pepper. To increase the heat of the salsa, use some or all of the seeds, depending on your preference, along with the flesh of the pepper.

MAKE AHEAD TIP: Cover and refrigerate for up to 1 day.