In a large mixing bowl, combine the shredded chicken, mayonnaise, Greek yogurt, Dijon mustard, red wine vinegar, garlic powder, onion powder, oregano, salt, and black pepper. Mix well until all ingredients are fully incorporated.

Add the diced celery, red bell pepper, green onions, parsley, and pepperoncini (if using) to the chicken mixture. Stir until evenly distributed.

Cover the bowl with plastic wrap and refrigerate for at least 30 minutes to allow the flavors to meld.

When ready to serve, slice the hoagie rolls in half and layer with lettuce leaves. Spoon the chicken salad generously onto the rolls.

Serve immediately, or wrap the sandwiches in foil for a picnic or lunch on the go.