This is a classic Greek side dish called spanakorizo. You can also dress it with a little lemon juice after it's cooked for brightness.
As a Greek-American family, we eat this often, especially during lent and as a main dish. To improve the cooking method given, try this: saute rice along with onion add minced fresh garlic too, then add boiling water, cover and simmer for about 10 minutes, then add spinach and tomato sauce, fresh parsley, fresh dill,salt and pepper. Cooked COVERED on low heat and add fresh lemon juice when it's done cooking. Beside the cooking directions, this recipe is authentic. - 10 Mar 2009 (Review from Allrecipes USA and Canada)
In Greece spanakorizo is a main dish, not a side - all the better to enjoy more of this healthy, delicious dish! fresh dill is essential to the recipe however - so much better than dried. Also, 1tbsp tomato paste is preferred in my family to tomato sauce -- you don't want the dish to be too tomato-y. Otherwise this recipe is spot-on. - 17 Feb 2007 (Review from Allrecipes USA and Canada)
This is a really good basic recipe. I normally add some garlic, use chicken broth instead of the water, chopped tomatoes instead of tomato sauce and omit the dill (not to fond of dill). I also add a bit of cumin and cinnamon for flavour. Last time I made it with bulgur instead of rice and it turned out great. Definitely serve with lemon and feta cheese. - 05 Feb 2006 (Review from Allrecipes USA and Canada)