In 12-inch skillet, place turkey and onion; sprinkle with salt and pepper. Cook over medium-high heat 4 to 6 minutes, stirring occasionally, until turkey is no longer pink.
Spray 3- to 4-quart slow cooker with cooking spray. In cooker, mix turkey mixture, salsa, beans, corn and chili powder.
Cover; cook on Low heat setting 6 to 7 hours.
To serve, heat taco shells in oven as directed on boxes. Stir cilantro into turkey mixture. Spoon about 1/4 cup mixture into each warm taco shell; top with lettuce and tomatoes.