Stir crushed tomatoes, 1 tablespoon lime juice, oil, chili powder, cumin, salt and pepper in a 4-quart slow cooker. Add onion and chicken breasts and turn to coat.
Cover and cook on high for 2 hours. Arrange pepper strips around the chicken and cover again.
Cook on high for 45 to 60 minutes more until the chicken reaches 165°F and the peppers are tender but still hold strips.
Lift chicken onto a plate, rest for 5 minutes and pull into thick shreds with two forks. Toss with the peppers and remaining lime juice, using tongs to leave excess liquid behind.
Warm tortillas in a dry skillet over medium heat for 20 to 30 seconds per side.
Divide the drained chicken and vegetables among 8 tortillas and serve 2 per portion.