Preheat oven to 400°F
Rinse and dry the chicken. Trim and excess fat or skin and clean the skin of any feathers. Set aside.
Add spices to a small bowl and stir together. If you have a mortar and pestle, give the spices a quick grind.
Add mayonnaise to the bowl and mix thoroughly.
Peel your onion and slice it in half. Insert both halves into chicken's cavity. Do the same with your lemon if you are using lemon. Tie the legs.
Rub the chicken with the mayonnaise mixture in a thin layer. Make sure to cover the crevices by the legs and wings. Keep the mayonnaise thin! Discard the leftovers. Place your chicken in the baking dish. Tuck the wings.
Place chicken on the center rack of your oven. Roast for 90 minutes (for a 6 lb chicken, if your chicken is smaller, refer to the table above). The chicken should be 165°F in the thickest part of the thigh.
Let your chicken rest at room temperature for 10 minutes before carving. Enjoy!