Chop the watermelon into uniform 1-inch cubes on a cutting board using a chef's knife. Arrange the cubes on a large serving platter or in a mixing bowl.
Peel and slice the avocados into evenly thick slices or cubes. Gently add them to the watermelon, being careful to maintain their shape.
Drizzle the lime juice evenly over the watermelon and avocado mixture to prevent browning and add freshness. Sprinkle lightly with salt.
Gently toss the salad with a large spoon or spatula until the ingredients are lightly combined, taking care not to crush the avocado slices.
Arrange the salad attractively on serving plates or bowls, showcasing the contrasting colors and textures.