Put the tomatoes, garlic cloves and basil in a food processor and process until the tomatoes are finely chopped but not smooth. Transfer to a large bowl and add the fennel seeds and oil. Season with salt and pepper. Leave the flavours to infuse for at least 15 minutes before cooking the pasta.
Cook the pasta in a large saucepan of salted boiling water according to the packet instructions until al dente. Drain, stir into the prepared tomato sauce, then toss in the mozzarella. Serve immediately.