Coat slow cooker with nonstick cooking spray, place 1 1/2 lbs chicken breasts in slow cooker, sprinkle chicken with 1/2 tsp garlic powder, salt and pepper to taste. Pour 8 oz salsa verde on top of chicken and cook on high for 2 hours. After 2 hours, take out chicken and shred. Discard half the liquid in the slow cooker, then put chicken back in slow cooker. Pour another 8 oz salsa verde on top of chicken and cook on low for another 2 hours. When done, drain chicken, reserving liquid to serve on the side.