Boil a large pot of water and cook the pasta according to the package directions.
While the pasta is cooking, make the pesto and cut the tomatoes, pepper, and olives into bite-sized pieces.
Drain the pasta when it’s done cooking and transfer it to a large bowl. Add the pesto and stir to coat well. Taste the pasta and sprinkle with salt if needed. Then stir in the tomatoes, bell pepper, olives, and mozzarella.
Serve warm or at room temperature. Store the leftovers in an airtight container in the refrigerator for up to 3 days. Yields 10 cups.