Heat the oven to 375°F and coat a 9-by-13-inch baking dish with the olive oil.
Whisk the rice, condensed soup, broth, mushrooms, onion, thyme, garlic powder and 1 teaspoon salt in the dish.
Season the chicken thighs with the remaining salt and black pepper and arrange them over the rice.
Cover the dish tightly with foil and bake until the rice is tender and the chicken reaches at least 165°F, 60 to 65 minutes.
Remove the foil and bake until the edges bubble and the chicken browns lightly, about 10 minutes.
Rest the casserole for 10 minutes, then fluff the rice around the chicken before serving.