In a saute pan over medium high heat, add oil, onion and garlic. Cook for 3 minutes then add rice. Toast for 3 minutes more. Transfer to 13x9 baking dish. Add chicken broth.
Preheat oven to 400degF.
In a saucepan over medium heat, add butter. Once melted, whisk in flour and let cook for 3 minutes. Whisk in chicken broth and cook for 3 minutes. Stir in mushrooms and onion soup seasonings mix. Cook another 3 minutes. Then add to baking dish. Stir to thoroughly combine.
Sprinkle both sides of chicken with onion seasoning mix. In the same saute pan you toasted the rice in, add chicken and cook on each side for 3 minutes. (just browning, not cooking through). Add chicken breast in single layer over rice mixture. Cover dish with aluminum foil and put in oven for 30 minutes.
Remove foil from baking dish and cook for another 15 minutes. Let stand for 5 minutes before serving a portion of rice and piece of chicken to each bowl.