If you want to skip the oven step, you can keep cooking on the stovetop once you return the meatballs to the dish. Turn the heat down to a gentle simmer and cook for about 10–15 minutes, until the risoni is cooked and the liquid has almost evaporated. Give it a stir every now and then to make sure it isn’t sticking on the bottom. Add the spinach and cheese in the last minute. Season and serve.