In a medium bowl, add the drained tuna, Greek yogurt, lemon juice, diced celery, diced red onion, chopped dill, and Dijon mustard. Sprinkle salt and pepper over the mixture.
Stir gently until all ingredients are well combined. Taste and adjust the seasoning if needed.
Serve immediately or chill for about 15 minutes to let flavors meld. Garnish with extra fresh dill. Enjoy with whole-grain crackers, veggie sticks, or as a sandwich spread.