Like any awesome salsa there is not a recipe for this other than:
Fresh Lime juice if wanted
Dice up your watermelon into small cubes. Mince your jalapeno (how ever many you want depending on your heat level) Mince your cilantro and Onion and toss all together.
The recipe doesn't call for Fresh Lime Juice and it actually doesn't need it since it isn't a citrus salsa but I'm a fresh lime juice addict and put it in everything. I just put a tiny bit so you couldn't even tell, I love that fresh liveliness it gives to it.
I used a chunk of watermelon you buy at the store next to all the cut up packaged fruit salad mixes. I didn't need a whole lot for just a few of us. It was the same price as an entire watermelon which sucks, but better that then have an entire watermelon go bad. I used one Jalapeno; half an onion and a couple tears of cilantro and just put them into my food processor buzzed it a few times until it was all very small. I don't like biting down on a big piece of onion or a jalapeno. Plus in this case the watermelon is the star and it shouldn't be hidden.
Eat this over anything meat, veggies whatever. I made Raspberry Chipotle chicken with this on top. TO DIE FOR!!
Travis and Dillion ate it with Hint of Lime Chips after dinner was done.