In a large bowl, whisk mayo, vinegar, salt, onion powder, and dijon mustard. Slowly whisk in olive oil. Season to taste with salt and pepper.
Add lettuce, tomatoes, red onion, blue cheese, parmesan cheese, bacon, and grilled chicken together, toss until combined with dressing. Season with salt and pepper.
Recipe by Cooking for Keeps at https://www.cookingforkeeps.com/chopped-tuscan-salad-made-salad-bar/