Season the chicken with garlic powder, oregano, cumin, and salt. Place it in the bottom of the slow cooker.
Pour half of the salsa verde (8 oz) over the chicken. Cover and cook on HIGH for 2 hours or LOW for 4 hours.
Remove the chicken and shred it using two forks.
Optional: Remove 2/3 cup of liquid from the slow cooker and discard it (or save it if you like extra sauce).
Return the shredded chicken to the crockpot with the remaining salsa verde. Adjust seasoning if needed, and keep warm until serving.