1. Peel, seed, and dice avocado and place in blender or food processor. Add garlic, salt, lime juice, vinegar, and cilantro leaves. With the machine running, slowly drizzle in oil until a creamy emulsion forms. Refrigerate.
2. Arrange the lettuce on a platter. Arrange the avocado and shrimp over the salad and drizzle with the vinaigrette on top. Serve right away.