Cover the eggs with about an inch of water in a medium pot. Bring to a boil, remove from the heat, cover and let stand for 8 minutes. Drain and submerge in ice water. When cool enough to handle, peel the eggs and chop.
Meanwhile, cook the bacon in a large nonstick skillet over medium heat until golden and crisp, about 4 minutes per side. Remove to a paper towel-lined plate. Crumble into bite-size pieces.
Whisk together the mayonnaise, sour cream, lemon zest and juice, celery, reserved tuna oil, three-quarters of the scallions, 1/4 teaspoon salt and several grinds of pepper in a medium bowl. Add the tuna and three-quarters of the bacon and egg and gently fold together (do not overmix). Season with additional salt and pepper if needed.
Sprinkle the tomato slices with salt and pepper.
Double-up the lettuce leaves and fill each with some tuna salad. Tuck in a tomato slice. Sprinkle with reserved scallions, bacon and egg.
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