Add the olive oil, dried Italian seasoning, fresh rosemary, paprika, garlic powder, cayenne, salt and pepper to a large mixing bowl. Mix to combine.
Add the chicken to the herb and seasoning mixture and combine until each piece of chicken is fully coated with seasoning. Set aside, or cover and allow the chicken to marinate overnight in the refrigerator.
Spray a large baking dish with non-stick cooking spray. Add the diced onion, garlic, olive oil, salt, cajun seasoning, chicken broth and water to the baking dish. Gently whisk to combine.
Add the rice to the baking dish and mix in with the broth.
Arrange the chicken thighs in the baking dish, directly on top of the rice. Cover baking dish with foil and bake, covered, for approximately 45 minutes. Remove the foil and bake for an additional 30 minutes, or until chicken is fully cooked and water has been absorbed.
Remove the chicken from the baking dish and transfer to a clean plate. Mix the rice and return the chicken to the dish. Cover with foil to keep warm.
As the rice and chicken rest, prepare the mushrooms.
Heat butter in a large skillet over high heat. Add the garlic and sauté for 1 minute or until fragrant. Add the mushrooms to the skillet and stir well to combine. Cook mushrooms until softened, approximately 5 minutes. Sprinkle with salt and pepper and fresh chopped parsley, if desired.
Transfer prepared mushrooms into the baking dish with the rice and mix well to combine. Best served warm. Enjoy.