Using an immersion blender or regular blender, blend your watermelon until juiced.
In a cocktail shaker, add ice, watermelon juice, lime juice, tequila, agave.
Add a few slices of jalapeno, depending on how spicy you want it.
Rim your glass with salt (or sugar if you prefer). I think salt works better for this one.
Pour your cocktail mixture into glass.
Add a few jalapeno slices on top and garnish with a slice of watermelon.
Tip: Take one of your jalapeno slices and rub around the rim of your glass for the perfect kick with each sip :)