Preheat the oven to 350 degrees F. Spray a 9-by-13-inch baking dish with nonstick spray.
Combine the rice, dried basil, garlic powder, 1/2 teaspoon salt (see Cook's Note) and a few grinds pepper in the baking dish. Add the diced tomatoes and tomato soup and stir to evenly disperse.
Place the chicken breasts on top of the rice mixture side-by-side in a single layer. Sprinkle the chicken breasts with 1/2 teaspoon salt and a few grinds of pepper. Sprinkle the onion soup mixture over the top of the entire dish, concentrating a little more heavily on the chicken (the onions will brown more evenly there and flavor the chicken).
Cover the baking dish tightly with aluminum foil and bake until the chicken and rice are cooked through, about 1 hour and 25 minutes. Let sit, still covered, for 15 minutes to allow the rice to absorb any remaining liquid. Uncover and serve.
The amount of salt in store-bought soup will vary from brand to brand, so feel free to season to taste. We found 1/2 teaspoon worked well in our tests.
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