Combine the seasoning mix ingredients in a small bowl.*
Rub outside of chicken with 1 tablespoon of olive oil and season with half of the seasoning mix. Place in a 9x13 inch baking dish, breast side up.
Toss the carrot, celery and onion with 1 tablespoon of oil and ½ the remaining seasoning mix. Arrange around the chicken.
Place the dish in the oven and roast for 15 minutes at 450°F.
While the chicken is roasting toss the cauliflower with remaining tablespoon of oil and seasoning mix.
After 15 minutes, turn the oven down to 350°F and bake for an additional 30 minutes.
Arrange the cauliflower around the chicken and bake 30-40 minutes more or until the chicken reaches 165°F in the thickest part of the thigh.
Remove from oven and place the chicken on a plate to rest 15 minutes.**
Notes
3 lb. chicken will need 15 minutes at 450°F plus an additional 60 minutes at 350°F. 4 lb. chicken will need 15 minutes at 450°F plus an additional 75-80 minutes at 350°F.*Take the chicken out of the refrigerator and let it warm up for about 30 minutes before seasoning it.**The vegetables can be returned to the oven to soften them if necessary.