Let's start! Put the oil in a wide bottom pan and add the onion. Bring to a heat and cook till the onion becomes soft. Add the cabbage and stir so it gets coated with the olive oil. Add the salt and pepper and stir again. Add the 900ml of water, the tomato sauce, and the sliced carrot and stir well. Cover and bring to a boil. When it starts boiling reduce the heat to medium low and simmer for about one hour or until the cabbage is soft. Add the rice and continue to simmer for 15 minutes more. If it needs more water you can add some. Remove from the heat and let it rest before serving. Serve with freshly ground pepper and feta cheese if you like. Enjoy!