Add watermelon chunks to a blender and blend until smooth.
Strain the watermelon puree through a fine mesh strainer to remove pulp.
Fill a cocktail shaker with ice.
Pour 2 oz watermelon puree, 1 oz tequila, 0.5 oz triple sec, and 0.5 oz lime juice into the shaker.
Shake vigorously for 15-20 seconds until well chilled.
Run a lime wedge around the rim of a margarita glass and dip in salt.
Fill the glass with ice and strain the cocktail mixture into it.
Garnish with lime and watermelon wedges.
Notes
Store extra watermelon puree in an airtight container for up to 3 days in the fridge.For a frozen version, blend the strained mixture with 1 cup of ice until smooth.Make it spicy by adding a few slices of jalapeño to the shaker.Skip the alcohol and substitute club soda for a refreshing mocktail version.