Add everything to the slow cooker: Place the chicken in the bottom of a 6-quart slow cooker. Top with the salsa verde, green chiles, sliced white onion (optional, see notes), garlic, olive oil, salt, cumin, chili powder, oregano, onion powder, and pepper.
2½ lbs boneless skinless chicken thighs, 1 (16 oz.) jar salsa verde, 1 (4 oz.) can diced green chiles, 4 cloves garlic, 1 Tbsp. olive oil, 1 tsp. kosher salt, 1 tsp. cumin, 1/2 tsp. oregano, 1/2 tsp. onion powder, 1/4 tsp. black pepper, 1 tsp. chili powder