Preheat the oven to 375 degrees F. Spray a 9 x 13-inch baking dish with nonstick cooking spray.
Add water, cream of mushroom soup, Italian seasoning, salt, garlic powder, and pepper to the prepared dish. Whisk until completely combined.
Stir in the uncooked rice, tomatoes, bell pepper, and onion.
Cover tightly with foil and bake for 35 minutes. Remove from the oven and stir in the sausage. Cover again, return to the oven, and bake for 20-25 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 the rice is done.