Boil and cool the eggs. Place eggs in a small pot, cover with cold water, bring to a boil, then turn off the heat and cover for 10–12 minutes. Transfer to an ice bath for 5 minutes, then peel and chop.
Prep the base. Drain the tuna thoroughly and break it up in a medium bowl with a fork. Excess liquid can make the salad watery, so press gently in the can if needed.
Add crunch and herbs. Stir in celery, red onion, and parsley or dill.
Dice them small so they blend evenly with the tuna and egg.
Make the dressing. In a separate small bowl, whisk Greek yogurt, mayonnaise, Dijon, lemon juice, garlic powder (if using), and a pinch of salt and pepper.
Combine. Pour the dressing over the tuna mixture. Fold gently until everything is coated. Add the chopped eggs last to keep some texture.
Taste and adjust. Add more lemon for brightness, more yogurt for lightness, or a little extra mayo for richness.
Season with salt and pepper to taste.
Serve your way. Spoon onto whole-grain toast, tuck into lettuce cups, pile over greens, or serve with crackers and sliced veggies.