Cook the pasta: Boil in well-salted water until just al dente. Drain and rinse briefly under cool water to stop cooking.
Shake off excess water.
Make the dressing: In a large bowl, whisk Greek yogurt, olive oil, red wine vinegar, lemon juice, Dijon, garlic, oregano, basil, salt, and pepper until smooth.
Taste and adjust: The dressing should be bright and a little salty. Add a splash more vinegar or a pinch of salt if needed.
Toss the pasta: Add cooled pasta to the bowl and coat evenly with the dressing.
Add the vegetables: Fold in tomatoes, cucumber, bell pepper, red onion, olives, and pepperoncini.
Finish with extras: Gently mix in feta and parsley. If using protein, add it now.
Chill and serve: Cover and refrigerate for at least 20–30 minutes.
Stir, taste, and adjust seasoning before serving.