This lovely and unusual salad blends color, texture and flavors in a most appealing way, balancing sweet-salty shrimp, tart grapefruit, mellow avocado and peppery arugula. A simple vinaigrette with a hint of ginger completes it. Try making your own vanilla bean vinegar, or substitute white wine vinegar if you'd prefer.
Make the vinaigrette by combining the first 6 ingredients in a glass jar. Close tightly and shake vigorously to combine. Let rest at room temperature for 1 hour to develop flavors.
Place the arugula in a large salad bowl and toss with about half of the vinaigrette. Divide the greens among 4 salad plates or arrange on a platter.
Place the shrimp in the salad bowl and add a tablespoon or two of the vinaigrette. Toss gently to coat the shrimp. Arrange the shrimp on top of the arugula.
Add the grapefruit segments and avocado slices to the salad, scattering them decoratively. Garnish with freshly ground pepper and serve immediately.