Add cream of mushroom soup and water to the prepared dish. Whisk together until completely combined.
Stir in uncooked rice, tomatoes, bell pepper, and onion. Season with about ½ teaspoon salt and ¼ teaspoon pepper. Stir again.
Cover tightly with foil and bake for 30 minutes. Remove from oven and stir in sausage. Cover again, return to oven, and bake for 30 more minutes.
At this point, give the casserole a stir and check the rice for doneness. If the rice isn’t completely tender, cover the dish and continue baking for 10-15 more minutes, or until most of the liquid is absorbed and rice is cooked.
Notes
Cooking Just for Two? Cut the ingredients in half and bake the casserole in an 8-inch square pan!*If you prefer to use raw Italian sausage, that will work too. You'll need to add it to the dish with all of the other ingredients at the beginning of your cooking time so that it has cooks through by the time the rice is done. Also, be aware that some of the grease from the sausage will be left in the dish (you can stir it in), so you might like to try raw Italian turkey sausage for a leaner option.