I usually make this with Chourico which is the Portugese version of Chorizo. Slightly different texture and flavor but both work well. To make it into a casserole for a full meal, I'll sometimes add pepper strips and frozen kale or spinach. Mushrooms are yummy but I have mushroom-phobic child so I can't ever add them :(
Heat oven to 350 degrees. Spray a large baking dish with cooking spray. Scrub potatoes and cut into quarters (eights if they are really huge). Place into a microwave safe bowl with a 1/4 cup of water. Cover and cook for three minutes.
While the potatoes are cooking, cut the sausage into small coins. Peel and cut the onion. Mix the cans of tomato sauce, diced tomatoes, sausage,and spices together. Put this mixture into the baking dish.
Drain the partially cooked potatoes and mix with the other ingredients in the baking dish. Cover the dish with foil and cook in the oven for 50 - 60 minutes. You may want to remove the foil after the first thiry minutes and let the dish cook uncovered if you'd like the sauce to reduce and to have some crispy bits of potato and sausage.