1. Snap off tough ends of asparagus spears. Steam asparagus, covered, for 3 minutes. Drain and rinse with cold water; drain.
2. Combine capers and the next 7 ingredients (through pepper) in a small bowl, stirring well with a whisk.
3. Place 1/4 cup juice mixture, cherry tomatoes, and beans in a small bowl; toss gently to combine.
4. Place 1 cup lettuce on each of 4 plates, and top each serving with 5 asparagus spears. Spoon about 1/2 cup white bean mixture over each serving, and divide tuna evenly among servings. Drizzle each salad with about 1 tablespoon remaining juice mixture.
Sustainable Choice: Buy solid white (albacore) tuna. Look on the label for sustainable pole-caught fish.
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