Remove and discard any packaged gizzards or pouches from the cavity of the chicken. (Or save them for chicken stock).
Transfer the chicken onto a baking sheet breast-side down.
Pat the chicken gently with paper towels to get rid of any excess moisture.
Make sure the chicken is breast-side down. Look for the base of the backbone at the opening of the bird. Now with your kitchen shears, cut along the side of the backbone until the end of it. Then cut along the other side of the backbone to remove it completely. You may have to give it some force since you're cutting through cartilage; crunching sounds are also to be expected.
After removing the backbone, store it safely for chicken stock instead of throwing it out!
With the backbone removed, carefully flip the chicken over and press down firmly on the breast bone to flatten the chicken into an even layer. You may hear the breastbone pop—that's normal; turn the thighs/legs outward.
Oil and season the bird, cook it, and enjoy!