Sandia en Fuego (a.k.a. the best Watermelon Margaritas of your life!) are a little bit spicy and a little bit sweet. This is going to be your cocktail of choice all summer long!
In a cocktail shaker, muddle the watermelon and the Serrano pepper. Add tequila, lime juice, and agave. Fill with ice. Shake until frosted and ice cold.
Salt rim of a rocks glass with volcanic salt. Fill with ice. Strain and pour over ice. Garnish with Serrano pepper slice and a watermelon cube.