Prepare the lettuce: Chop the romaine lettuce into bite-sized pieces. Wash and dry it well, preferably using a salad spinner, so the dressing does not get watered down.
Chop the vegetables: Dice the cucumber, red onion, and bell pepper. Halve the cherry tomatoes, slice the Kalamata olives, and chop the parsley. Wait to dice the avocado until just before serving.
Make the dressing: In a small bowl or jar, whisk together the olive oil, lemon juice, red wine vinegar, minced garlic, fresh oregano, Dijon mustard, salt, and black pepper until combined.
Assemble the salad: Add the chopped lettuce, chickpeas, cucumber, cherry tomatoes, red onion, bell pepper, Kalamata olives, feta cheese, and parsley to a large salad bowl.
Dress the salad: Just before serving, dice the avocado, add it to the salad, drizzle with the lemon-Dijon dressing, and toss gently.
Toss and serve: Gently toss until everything is evenly coated. Serve immediately while the lettuce is crisp and the avocado is fresh.