Prepare the Tuna: Open and drain the cans of solid white albacore tuna, then flake into a mixing bowl.

Mix the Dressing: In a separate bowl, combine Greek yogurt, Dijon mustard, lemon juice, and sweet pickle relish, seasoning with salt and pepper. Whisk until smooth.

Add Fresh Ingredients: Chop celery, dice red onion, and wash fresh dill. Mix these into the flaked tuna.

Combine Everything: Fold the dressing into the tuna mixture until well-coated without over-mixing.

Chill for Best Flavor: Cover and refrigerate for at least 30 minutes to enhance flavor.

Assemble the Sandwich: Layer lettuce on whole-grain bread, add tuna salad, top with tomato slices, and finish with another slice of bread.