Brine

Pour about 1/3 of the water into a large pot (large enough for the brine and submerged chicken, I used my dutch oven) with remaining ingredients. Bring to high simmer and stir for about a minute to to dissolve salt.
Remove from heat, pour in remaining water. Cool completely before using. Do not put the chicken in before the liquid is cool — this is a health hazard.
Submerge chicken in cooled brine, cover and refrigerate for 12-24 hours.

Roasting Brined Chicken

Remove chicken from brine and pat dry with paper towels to remove excess moisture. Reserve the lemon and onion quarters to roast alongside the chicken. Allow chicken to come to room temperature before seasoning - about half an hour.
Preheat oven to 450°F. Once chicken is room temperature (this will ensure even cooking), season the chicken (on both sides) with cajun seasoning and a small pinch of salt (the chicken will be salted from the brine). Place in a cast iron pan, breast side up, and surrounded by reserved lemon and onion.
Turn down the oven to 350°F, then roast the chicken for 50 minutes to 1 hour or until the internal temperature at the joint between the leg and thigh is 165°F. Remove chicken from the oven, squeeze with roasted lemon, and rest for 10 to 15 minutes before carving.

Perfect Roast Chicken

Mongolian Beef