12 corn tortillas (6 inches) or taco shells, warmed
Optional toppings: shredded cheddar cheese, shredded lettuce and chopped tomatoes
Place chicken in a Dutch oven; add water to cover. Bring just to a boil. Reduce heat; simmer, uncovered, for 10-12 minutes or until a thermometer inserted in chicken reads 180°.
Using tongs, remove chicken from pan; reserve 1/2 cup cooking liquid. Cool chicken slightly. Shred when cool enough to handle.
In a large saucepan, heat oil over medium heat. Stir in flour until smooth; cook and stir until golden brown, about 2 minutes. Gradually whisk in reserved cooking liquid. Bring to a boil; cook and stir 2 minutes longer.
Stir in tomato sauce and seasonings; return to a boil. Stir in shredded chicken; heat through, stirring occasionally. Serve in tortillas with toppings if desired.