In a cocktail shaker, muddle together watermelon and mint leaves. Add tequila, lime juice, agave syrup, and saline solution (or fine-grain table salt). Fill the shaker past the top of the liquid with ice, close, and shake together.

Rub the cut side of one of your juiced limes around the edge of a chilled double rocks glass and coat the rim with chili lime seasoning.

Place a large ice cube into the glass and strain the watermelon mixture over the cube. Use a bar spoon to scoop the pieces of watermelon and lime into the glass and give a quick stir.

Garnish with any mix of watermelon, mint, and lime, if desired.