Cook pasta according to instructions.
Meanwhile heat 1 tablespoon of olive oil oil in a large skillet or saucepan on medium-high heat.
Crumble sausages (Note 1) into skillet and cook for 3-5 minutes, until browned on all sides. Take the sausage out of the skillet and set aside for later.
Clean skillet if necessary and heat the remaining tablespoon of olive oil on medium heat.
Add in the diced onion to the skillet and cook for 2-3 minutes, until translucent, then add in the minced garlic and cook for another 2-3 minutes, being careful not to burn garlic.
Stir in the diced tomatoes, salt, pepper and Italian seasoning. Bring to a simmer and then turn down the heat to medium-low. Simmer for 8-10 minutes until most of the liquid from the tomatoes is gone.
Mix the crumbled sausage back into the sauce. Cook for another 2-3 minutes to heat the sausages back up, then turn off the heat
If the skillet or saucepan is large enough add the cooked pasta to it, otherwise combine sauce and pasta together in a large bowl. Mix the sauce and pasta together, until the pasta is well coated in the sauce.