Drain the tuna thoroughly by pressing it against the can with a fork, then transfer to a large mixing bowl and flake with a fork.
Prepare the vegetables: slice cucumbers into half-moons (leaving some skin on for color) and chop celery into bite-sized pieces. Add both to the bowl with tuna.
In a separate small bowl, whisk together mayonnaise, Greek yogurt, lemon juice, Dijon mustard, honey, garlic powder, and a pinch of salt and pepper until smooth and creamy.
Pour the dressing over the tuna and vegetables. Add chopped dill and parsley.
Gently fold everything together until evenly coated, being careful not to crush the tuna or vegetables.
Taste and adjust seasoning with more salt, pepper, or lemon juice as needed.
Cover and refrigerate for at least 30 minutes to allow flavors to meld.
Give the salad one final gentle stir before serving chilled.