In a medium skillet, combine turkey, tomato sauce and chili powder. Simmer over medium heat, breaking up meat with a spoon. Cook about 5-7 minutes, or until turkey is cooked to 165° F using a meat thermometer.
Meanwhile, bake tostada shells in oven until crisp, about 6 minutes.
In a bowl, toss cabbage with lime juice, oil and cilantro.
Place a layer of turkey mixture on each tostada. Top with cabbage mixture and sprinkle with tomatoes.
Note: For food safety, cook turkey to a minimum internal temperature of 165°F as measured by a meat thermometer.