Preheat the oven to 350°F. Coat a 13x3x9-inch baking dish with olive oil.
In a large nonstick skillet over medium heat, cook the onion in the oil for 3 minutes. Add the turkey. Cook, stirring and breaking up the meat with a spoon, for about 6 minutes, or until the turkey is no longer pink. Add the beans and chili powder. Cook, stirring occasionally, for 4 minutes.
Place 6 tortillas, overlapping, in the bottom of the baking dish. Spoon the turkey mixture evenly over the tortillas. Cover with the remaining 6 tortillas. Sprinkle with the cheese. Spoon on the tomatoes and enchilada sauce. Bake for 1 hour.
Makes: 6 to 8 servings (407 calories per serving)