Slice the watermelon into uniform cubes approximately 1-inch in size using a sharp chef's knife and cutting board. Transfer the cubes to a large mixing bowl.
Using the same knife and cutting board, peel the avocado, remove the pit, and slice it into thin, even pieces. Carefully place the avocado slices over the watermelon cubes in the bowl.
Gently toss the watermelon and avocado slices together, just enough to combine the flavors without breaking the avocado. Observe the vibrant colors and contrasting textures.
Arrange the mixture onto individual serving plates in a decorative pattern. Garnish with fresh mint leaves for added aroma and visual appeal.
Serve immediately to enjoy the crisp, cool watermelon and creamy avocado combination at its best. The final dish should appear colorful and inviting, with the vibrant red and green contrasting textures.