Place tuna in a bowl with celery, cucumber, and red onion. Stir to combine.
In a small bowl, whisk together Greek yogurt, lemon juice, salt and pepper. Add dressing to tuna mixture. Stir to combine.
Remove the core of each tomato and gently scooping out the seeds inside. Carefully stuff the tomatoes with about 1/3 cup of tuna salad. Sprinkle the freshly chopped chives on top of the tomatoes.
Serve immediately.
Recipe Notes
This is a great salad to make a double batch of to eat throughout the week.