Use a chef's knife and cutting board to cut the watermelon into roughly 1-inch cubes, ensuring even size for consistency. Arrange the cubes in a mixing bowl.
Peel and pit the ripe avocado, then slice into thin, even pieces. Gently add the avocado slices to the bowl with the watermelon.
Drizzle the lime juice over the fruit mixture, then sprinkle with a pinch of sea salt and freshly ground black pepper. Toss gently using a spoon or salad tongs until the ingredients are coated evenly, taking care to not mash the avocado.
Once mixed, transfer the salad to a serving plate or bowl for display. Observe the vibrant contrast of red watermelon and green avocado, with the fruit remaining intact and slightly glistening from the lime juice.
Serve immediately to enjoy the fresh, juicy textures of the watermelon and the creamy smoothness of the avocado. Optionally, garnish with additional lime wedges or fresh herbs.