Heat the oil in a saucepan with a lid, when hot, add the rice and the onion. Sauté until the rice just begins to turn opaque, about 5 minutes; add the tomato sauce and broth or water, along with about ½ teaspoon salt. Stir, cover, lower the heat, and cook for 25 minutes, or until the liquid is absorbed (don’t peek, just let it cook); uncover, fluff with a fork, taste and adjust salt. Top with Cotia cheese, if desired. Serve immediately.