1. Whisk together lime juice, oil and lime zest. Set aside.
2. Place watermelon cubes in single layer in large shallow dish. Pour lime juice mixture over watermelon, and gently toss to combine. Cover, and refrigerate until ready to serve.
3. Place 5 jalapeño rings each in 4 shallow serving bowls. Mound 1/2 cup watermelon in center of each bowl. Divide marinade among bowls. Sprinkle with basil, sesame seeds and salt, and serve.