1Mix jalapeño chili, garlic, chili powder, oil, lime juice and salt in 3- to 4- quart slow cooker. Add chicken; coat with oil mixture.
2Cover and cook on low heat setting 8 to 10 hours.
3Remove chicken from cooker; place on cutting board. Shred chicken, using 2 forks. Return chicken to cooker and mix well. Using slotted spoon to remove chicken mixture from cooker, place 1/3 cup chicken mixture on each tostada shell. Top with lettuce, cheese, salsa and sour cream.