Here's my photo. I glazed the watermelon with a mixture of honey, lime juice, salt and a little ancho chile powder. Garnished with a chiffonade of mint.
All sounds good, but it didn't work. None of us cared for it.
For one thing, as other reviewers have mentioned, grilling the watermelon changes the texture of it; it gets mushier.
Much better just plain sliced! Live and learn!
Lee