Cook the pasta: Bring a large pot of salted water to a boil. Add pasta and cook until just tender (al dente), 1–2 minutes less than the package suggests so it holds up after chilling.
Rinse and cool: Drain the pasta and rinse under cold water to stop the cooking.
Shake off extra water so the dressing doesn’t get watery.
Make the dressing: In a large bowl, whisk Greek yogurt (and mayo if using), lemon juice, Dijon, garlic powder, onion powder, salt, and a pinch of pepper. Taste and adjust salt or lemon.
Prep the mix-ins: Flake the drained tuna with a fork. Finely chop cucumber, shred carrot, and measure corn.
Chop pickles and herbs if using.
Combine: Add cooled pasta and tuna to the bowl with dressing. Gently fold to coat. Add cucumber, corn, carrot, pickles, and herbs.
Stir until evenly mixed.
Adjust texture: If it looks too thick, drizzle in 1–2 tablespoons olive oil or a splash of water or milk to loosen.
Chill: Cover and refrigerate for at least 30 minutes to let flavors meld. It firms up as it chills.
Serve: Give it a quick stir. If it seems dry, add a spoonful of yogurt or mayo and a squeeze of lemon to refresh.
Serve cold or slightly cool.