Cook pasta shells according to package directions, omitting salt and fat.
While pasta cooks, heat a large nonstick skillet over medium-high heat; add oil. Add mushrooms and garlic; cook 4 minutes or until tender.
Stir in tomatoes and next 4 ingredients; bring to a boil. Reduce heat; simmer, stirring occasionally, 20 minutes or until slightly thick. Remove from heat. Let stand 5 minutes.
Preheat oven to 350°.
Spoon 1/4 cup sauce into an 11 x 7-inch baking dish coated with cooking spray.
Spoon sauce evenly into cooked shells. Arrange shells in baking dish. Sprinkle with cheese and parsley.
Cover and bake at 350° for 20 minutes or until bubbly and cheese melts.