Step 1: Prep the vegetables by washing the romaine and radicchio, ensuring they are completely dry before chopping. Slice the cucumber, tomatoes, and red onion.
Step 2: To mellow the red onion, soak the slices in a bowl of ice water for 10 minutes, then drain and pat dry.
Step 3: Prepare the dressing by whisking together the olive oil, red wine vinegar, minced garlic, dried oregano, Dijon mustard, salt, and pepper in a small bowl or jar until emulsified.
Step 4: In a large salad bowl, combine the dried greens, tomatoes, cucumber, onions, olives, and pepperoncini.
Step 5: Just before serving, drizzle the dressing over the salad and toss gently to coat all ingredients evenly.
Step 6: Top with shaved Parmesan cheese and croutons, then serve immediately for maximum crispness.