Step 1

Preheat oven to 400 degrees F. Toss together bread and oil in a large bowl; spread in a single layer on a rimmed baking sheet. Bake in preheated oven until golden brown and toasted, about 10 minutes, stirring once halfway through cooking. Set aside to cool.

Step 2

While bread toasts, whisk together yogurt, water, mayonnaise, Parmesan, mustard, salt, and pepper in a large bowl. Cut 5 inches from the top of each romaine lettuce heart; set aside 8 of the largest leaf tops for lettuce cups. (Save remaining leaves for another use or discard.) Chop bottom section of each romaine lettuce heart into bite-size pieces. Add chopped lettuce, chicken, and cooled bread to bowl with dressing; toss to coat. Divide evenly among 8 reserved lettuce cups.