Cook the pasta: Bring a large pot of salted water to a boil. Cook pasta according to package directions until al dente.
Drain and rinse under cold water to cool and stop the cooking.
Dry the pasta: Shake off excess water and spread the pasta on a tray or large bowl so it doesn’t steam. A drier pasta surface helps the dressing cling better.
Make the dressing: In a bowl, whisk together Greek yogurt, mayonnaise, 2 tablespoons milk, lemon juice, Dijon, garlic powder, onion powder, dill, parsley, chives, salt, and pepper. Adjust thickness with more milk, a splash at a time.
You want it creamy but pourable.
Prep the veggies: While the pasta cools, chop tomatoes, cucumber, bell pepper, red onion, and herbs. Drain corn and olives if using.
Toss it all together: In a large bowl, combine pasta, veggies, olives, and cheese (if using). Pour over about two-thirds of the dressing and toss gently to coat.
Taste and adjust: Add more dressing, salt, or pepper as needed.
A squeeze of lemon brightens the flavors if it tastes flat.
Chill: Cover and refrigerate for at least 30 minutes so the flavors meld. Reserve any extra dressing to freshen it up before serving.
Serve: Toss again just before serving. If it looks a bit dry after chilling, add a spoonful of the reserved dressing or a splash of milk.