For added flavor I also sautéed chopped onions, Italian parsley and shiitake mushrooms. With a little more energy I could have added broccoli florets sliced thin and tomato sauce and that's what I will do next time I make the dish.
Earlier in the day I had made ground pork meatballs with an egg, bread crumbs, chopped an Italian parsley and chopped onions. I added those at the end because, why not? Sausages and meatballs together on pasta, come on, that's crazy delicious!
A couple of general suggestions.
For the spaghetti (or penne or fussili) buy a high quality Italian brand. I love Borella. The pasta has a clean taste, with a good bite. 
For the sausages, you can use any kind of sausage you like. I prefer pork suasages with fennel made by Monte Carlo (3103 W. Magnolia Blvd
Burbank CA 91505), an Italian deli in the San Fernando Valley. That's a long drive from where we live in Pacific Palisades, but when I am already in the Valley, I'll stock up and buy five pounds.
I'm not going to eat five pounds of sausages all at once. Freezing keeps them "fresh" and available. To freeze the sausages, I dredge each sausage in olive oil, then I wrap each sausage in plastic wrap before placing the wrapped sausages into a sealable plastic bag. Even months later, the sausages taste fresh and delicious.
There are many ways to saute the sausage. My preference is to first remove the casing, then using my fingers, I create quarter sized chunks of sausage. That way each piece of sausage has a crisp outside.
Use a carbon steel or cast iron frying pan for best results.
The recipe is for one. If you want to make the dish for two, double the ingredients and so on for as many people as you like.
Pasta with Italian Sausage
Serves one
Time to cook 25 minutes
Ingredients
1 Italian sausage or any sausage you enjoy
1/4 package of pasta, any shape you enjoy
2 tablespoons chopped yellow onions, washed, peel removed
2 tablespoons chopped Italian parsley, washed, leaves only
2 large shiitake mushrooms or a mushroom you enjoy, washed, end of the stem removed, thin sliced
4 tablespoons extra virgin olive oil, a good quality brand, preferably from Italy
1 teaspoon kosher salt, preferably Diamond Crystal Kosher Salt, do not use any salt that has iodine
1 garlic clove, washed, peeled, finely chopped (optional)
1/4 cup pasta water, reserved from cooking the pasta
1/2 cup freshly grated Parmesan cheese
Directions
Place a large carbon steel or cast iron frying pan on a medium flame.
Add 1 tablespoon olive oil.
Sauté the chunks of sausage without the casing until browned on all sides. Remove from the pan. Drain on a paper towel on a plate.
Discard the oil in the pan.
Add 1 tablespoon of olive oil. Heat on a medium flame.
Add the vegetables. Sauté until lightly browned.
Return the cooked sausages to the pan. Remove from the heat and set aside.
Fill a large pot with water. Season with kosher salt. Place on the stove on high heat. Bring to a boil.
Add pasta and stir well to prevent the pieces of pasta sticking together.
Cook 10 minutes or until al dente.
As you drain the pasta in the sink, capture 1/4 cup of pasta water.
Add the pasta water and cooked pasta to the sautéed vegetables. Drizzle the remaining olive oil over the pasta and vegetables.
Heat on a medium flame.
Toss well and reduce the liquid so the sauce coats the pasta.
Plate the pasta and top with freshly grated cheese.
Serve hot.
