Cook tortellini according to package directions; drain. Return to saucepan.
Meanwhile, place roasted sweet pepper in a food processor. Cover and process until almost smooth. Set aside.
For sauce, in a medium saucepan cook the onion and garlic in hot oil until tender. Add pureed peppers, basil, sugar, and salt. Cook and stir until heated through. Pour sauce over tortellini; toss to coat.