Scoop 2 cups each from the watermelon and the cantaloupe using a melon baller. Carve the remainder of the watermelon out and reserve shell.
Add to a blender the chopped mint, chopped basil, lemon juice, simple syrup and amaretto. Blend until smooth.
Add the watermelon and cantaloupe balls to the carved-out watermelon half.
Add the vinaigrette to the balls and toss to combine.
Garnish with the mint and basil sprigs and taste.