Heat the oil in a large nonstick frying pan over moderate heat. Cook the onion and garlic for 5 minutes or until soft. Add the tomatoes, tomato pasta sauce, dried chilli and a pinch of salt. Simmer for 10 minutes.
Meanwhile, cook the tortellini in a large saucepan of boiling water according to the packet directions, until firm-tender. Drain and toss with the sauce.