Add onion, garlic, black beans, lime juice, and orange juice to a slow cooker. Season chicken breast with Carne Asada Seasoning and add to the slow cooker. Cover and cook on high for 4 hours or low for 6 hours, until chicken is very tender. Alternately, cook ingredients in an electric pressure cooker for 25 minutes. Use quick release.
Shred chicken and toss with sauce in the slow cooker.
Meanwhile, prepare rice according to package directions.
Serve shredded chicken over prepared rice with toppings such as avocado, cheese, and cilantro.
