Heat oven to 375° F. Spray 13- x 9-inch baking dish with nonstick cooking spray; set aside. Heat oil in medium saucepan over medium heat. Stirring constantly, add flour and cook 1 minute. Slowly add chicken broth, whisking until smooth. Stir in tomato paste, chili powder, oregano, cumin and salt. Bring to a boil. Reduce heat; cook 10 minutes or until slightly thickened.
Meanwhile stir together chicken, 1 cup shredded Mexican 3 cheese and onion. Divide mixture evenly into center of each tortilla. Roll up tortilla tightly; place in pan. Pour sauce over tortillas.
Cover; bake 15 minutes. Uncover; top with remaining cheese. Bake 5 minutes or until cheese is melted.