Preparation Combine shallot, vinegar, and 1 tsp. salt in a blender jar. Let sit 5–10 minutes to lightly pickle. Meanwhile, cook green beans in a large pot of boiling salted water until crisp-tender, about 4 minutes. Drain, then run under very cold water until cool to the touch. Add basil, oil, lemon juice, and pepper to shallot mixture and blend until mostly smooth. Pour dressing into a large bowl. Add green beans, lettuce, white beans, parsley, and capers and toss with your hands to coat. Add tuna and gently toss to combine. Transfer salad to a platter.
Preparation Combine shallot, vinegar, and 1 tsp. salt in a blender jar. Let sit 5–10 minutes to lightly pickle. Meanwhile, cook green beans in a large pot of boiling salted water until crisp-tender, about 4 minutes. Drain, then run under very cold water until cool to the touch. Add basil, oil, lemon juice, and pepper to shallot mixture and blend until mostly smooth. Pour dressing into a large bowl. Add green beans, lettuce, white beans, parsley, and capers and toss with your hands to coat. Add tuna and gently toss to combine. Transfer salad to a platter.