For the Ginger Dressing, mix the mayonnaise in a small bowl with the vinegar and water or orange juice. Whisk in the oil in a slow, thin stream. Press each ginger slice in a garlic press over a small glass, yielding about 2 teaspoons of juice. Add the ginger juice to the dressing to taste. Season with salt and pepper. (This can be prepared ahead, covered and set aside at room temperature for about 2 hours or refrigerated until 1 hour before serving.) Cook corn kernels in a pot of simmering water for 5 minutes; drain. (This can be prepared ahead and set aside at room temperature.) Place a heavy small nonstick skillet over medium heat and film it with oil. Add the shrimp and cook until just pink, for about 2 minutes total, turning with tongs halfway. (This can be prepared ahead and set aside at cool room temperature for several hours.) To serve, mix the corn and salad greens in a large bowl. Gently toss with enough dressing to coat lightly. Mound the salad in the center of 4 or 6 large plates. Mix the shrimp with several tablespoons of the remaining dressing to coat lightly. Arrange the shrimp around the salad. Sprinkle the salad with green onions. Serve immediately.