Preheat the oven to 375°F (190°C) and lightly spray a 9x13-inch baking dish with nonstick spray.
In the prepared dish, combine 2 1/2 cups chicken broth, 1 cup white rice, 3 tablespoons lemon juice, 3 tablespoons melted butter, 1 tablespoon lemon zest, 1 tablespoon minced garlic, 1 teaspoon onion powder, 1 teaspoon salt, 1 teaspoon dried basil, 1/2 teaspoon pepper, and 1/2 teaspoon dried thyme; stir to distribute evenly.
Season the cubed (1 pound) chicken breasts with 1 teaspoon salt and 2 teaspoons lemon pepper, then nestle the seasoned chicken into the rice mixture in an even layer.
Bake uncovered for 30 minutes at 375°F (190°C).
Remove from the oven, arrange thin slices from 1 lemon over the top, return to the oven, and bake an additional 5 minutes until the rice is tender and the chicken is cooked through (no pink remains).
Let the casserole rest for 5 minutes before serving.