Place the watermelon cubes in a large mixing bowl. Ensure they are evenly spread out for easy mixing later.
Peel the avocado with a vegetable peeler, then cut it in half, remove the pit, and slice into thin, even pieces. Arrange the slices on top of the watermelon or set aside.
In a small bowl, whisk together the olive oil, fresh lemon juice, honey (or agave), sea salt, and black pepper until the dressing is well combined and slightly emulsified.
Pour the dressing over the watermelon and avocado slices. Gently toss with a large spoon or spatula until all ingredients are evenly coated without breaking the avocado slices, visualized by a light sheen on the fruit and a gentle mix.
Transfer the salad to a serving plate or bowl. Garnish with additional slices of avocado or a sprig of mint if desired. Serve immediately for maximum freshness and visual appeal.