FOR THE DRESSING: In a glass jar, or container with a tight fitting lid, add garlic, salt, pepper, oregano, lemon juice, oil, yogurt and mayonnaise. Shake until all ingredients are combined. Refrigerate until ready to use. This dress may need to be shook or stirred before serving.
FOR THE SALAD: Clean chopped lettuce and spin dry (if you have a salad spinner) or pat dry. Divide lettuces among bowls or plates and top with slices of grilled chicken, then the tomatoes, some chickpeas, red onion, beets, olives, pepperoncinis, feta cheese and coarsely ground black pepper.
Drizzle the creamy Greek dressing over top and serve alongside warm pita bread.