Preheat oven to 375°. Spray shallow 2-quart baking dish with no-stick cooking spray; set aside.
Heat 1 tablespoon oil in 3-quart saucepot over medium heat and cook onion, stirring occasionally, until tender, about 5 minutes. Add 2 tablespoons oil and flour and cook, stirring constantly, until flour is toasted, about 1 minute. Gradually stir in broth. Bring to a boil. Boil until thickened, about 1 minute. Stir in Sauce, macaroni and spinach. Turn into prepared pan. Cover tightly with aluminum foil. Combine bread cubes and remaining 1 tablespoon oil in medium bowl, then arrange on top of foil.
Bake, stirring bread cubes once, 20 minutes or until toasted and pasta is bubbling. Remove foil, then evenly top with toasted bread cubes.