To prepare enchilada sauce: In a small saucepan, heat oil over medium heat. Stir in flour; cook and stir 1 minute. Stir in chili powder and oregano; cook and stir 30 seconds more. Stir in tomato sauce, water, and salt. Bring to boiling; reduce heat. Simmer, uncovered, 8 to 10 minutes or until slightly thickened, stirring occasionally.