Spray the bottom of the slow cooker with cooking spray.
Place the chicken breasts in the bottom of the slow cooker in a single layer.
Sprinkle the chicken evenly with the cumin, garlic powder, onion powder, and salt.
Pour the salsa verde over the seasoned chicken, covering it as much as possible.
Cook on low for 6 hours or on high for 3 hours, until the chicken is fully cooked and tender.
Remove the chicken to a cutting board and shred with two forks.
Return the shredded chicken to the slow cooker and stir to combine with the cooking juices.
Serve warm in flour or corn tortillas with desired toppings such as diced tomato, avocado, cheese, sour cream, or chopped cilantro.