Combine beans, tuna, bell pepper, onion, parsley, capers, rosemary, 1/4 cup lemon juice and 2 tablespoons oil in a medium bowl. Season with pepper. Combine the remaining 1/4 cup lemon juice, 2 tablespoons oil and salt in a large bowl. Add salad greens; toss to coat. Divide the greens among 4 plates. Top each with the tuna salad.