Rinse cucumbers. Peel off skin every ¼ inch, all the way around. Cut lengthwise. Scoop out the seeds with a small spoon.
Rinse lemon. Zest using the small holes of a box grater. Cut in half. In a small bowl, squeeze juice. Discard seeds.
Rinse and chop green onions.
Drain tuna. In a colander, drain and rinse beans.
In a medium bowl, mash beans lightly with a fork.
Add green onions, tuna, oil, mustard, salt, pepper, lemon zest, and 2 Tablespoons of the lemon juice to beans. Mix with a fork.
Fill each cucumber half with ¼ tuna mixture. Serve.
Chef’s Notes
For a snack or party food, cut cucumbers into thick slices. Do not remove seeds. Place a dollop of tuna mixture on top.
Add chopped bell pepper or celery for extra nutrition and crunch.
Try canned salmon, packed in water, instead of tuna.
To ensure this recipe is truly gluten-free, use ingredients labeled "certified gluten-free." Some foods, like oats or soy sauce, can contain traces of gluten depending on the brand or processing methods.