The best and quickest way to cook a whole chicken.
Preheat the oven to 425F.
Using kitchen scissors, cut down each side of the chicken's backbone. <--This is on the underside of the chicken, not the breast side. Remove the backbone from the chicken, and keep it to make broth/stock later, or discard it.
Place the chicken, breast side up, on a cutting board and press down on the chicken until it lies as flat as possible.
Place the onion slices in the center of the sheet pan, or a large oven-safe skillet (such as a cast iron skillet). Place the chicken, breast side up, over the onions. Drizzle the oil over the chicken, rubbing the oil over the chicken skin.
Generously sprinkle the chicken skin with salt and pepper.
Cook the chicken, uncovered, for 50-55 minutes, or until the skin is brown and the juices from the chicken run clear (when the area between the leg and thigh are cut).
Allow the chicken to rest for about 10 minutes before cutting and serving, or storing in a container for meals later in the week.
If you're prepping this chicken in advance, or have leftover meat, here are some ideas: chicken salad (curry or deli-style), chicken noodle soup (could also make this on the stove-top), nachos, chicken pot-pie, an addition to salads, a lunchmeat alternative.
Want to try something different? Try this barbecue spatchcock chicken from Raising Generation Nourished.