Heat oven to 375°F. Spray 3-quart casserole with cooking spray.
In 12-inch skillet, heat oil over medium heat; stir in onion, garlic and turkey. Cook, stirring frequently, until meat is no longer pink, about 5 minutes. Stir in tomato pasta sauce.
Meanwhile, cook tortellini in 3-quart saucepan in boiling water until pasta is done; drain. Toss cooked pasta with tomato mixture. Spoon into casserole. Sprinkle with cheese.
Bake uncovered 20 to 25 minutes or until hot. Let stand 5 minutes before serving.