Combine basil and pine nuts in a food processor and pulse until coarsely chopped.
With the blade running, add the oil in a long, smooth stream and process until smooth.
Season with salt and pepper and stir in the parmesan cheese.
In a large bowl, combine the chicken, yogurt, 1/3 cup pesto, and salt and pepper, to taste.
Layer mixture on your toasted rolls, along with spinach, tomato, and fresh mozzarella.