Add 2-3 cups of diced watermelon in a blender and blend until smooth. Strain watermelon juice and add to a pitcher. Mix in tequila, triple sec, and the juice of one lime and stir.
Fill a champagne glass half way with melon mixture and the rest with champagne.
Recipe by Fig & Thyme at https://www.figandthyme.com/melon-rita-mimosa/