Add the chicken breasts to the slow cooker.
Pour the salsa verde over the chicken, then add the diced onion, minced garlic, cumin, salt, and black pepper.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the chicken is tender and easy to shred.
Use two forks to shred the chicken directly in the slow cooker and stir it into the sauce so it absorbs the flavors.
Spoon the shredded chicken mixture over cooked rice. Add black beans, then finish with shredded cheddar cheese, sliced avocado, fresh cilantro, and a squeeze of lime.