You can use any vegetable you like raw instead of these–broccoli, cauliflower, snow peas, etc. would all be good. Just chop them all about the same size. You can prepare the veggies in advance, but keep the lettuce separate from any watery ones, such as tomatoes, and assemble the salad just before serving.
Leaving the base attached, cut the romaine heart lengthwise three times; rotate it a quarter of a turn and make two or three more cuts. Then slice it from top to the base so that you have small, bite-sized pieces. Wash it in a strainer or salad spinner and then spin well to dry.
Place the romaine into a large bowl and add other vegetables, chickpeas, and olives. Add the vinaigrette and mayo to taste, being careful not to add too much, as well as a generous grating of black pepper, and toss to combine. Sprinkle with walnuts and serve.
If omitting olives, deduct 12 calories and 1.2g fat; if omitting walnuts, deduct 12 calories and 1.22g fat per serving.