With a fork prick all the sausage links all over.
Bring a pot of water to a boil. Add the sausage and boil for 10 minutes. Remove to a plate slice the links into bite sized chunks.
Preheat the oven to 450 degrees
Transfer to a baking dish and add the potatoes, tomatoes, onions, oil and salt. Toss to make sure everything is coated in oil. Sprinkle with the Parmigiano Reggiano cheese. Pour water into the pan.
Bake for 45-55 minutes or until the potatoes are fork tender and the sausage has cooked.