Cook penne pasta according to instructions until it's al dente. Drain and set aside once done.
Heat up a large skillet over medium-high heat and in 1 tsp of olive oil. Add in the sausage and cook until they brown up. Should take around 5-8 minutes. Add a little bit of water the sausages start sticking to the skillet.
Remove the sausages from the skillet and place them on a chopping board, let them cool down.
Remove any remaining water from the skillet and add 1 tbsp of olive oil. Add in the sliced red onion and cook for about 2 minutes. Then, add in Italian seasoning, fennel seeds, and crushed chili pepper flakes. Stir to cover the onion with spices.
Now add in minced garlic and tomato paste, stir, and sauté for a couple of minutes.
Then add in tomatoes and red bell pepper and cook for another 3-4 minutes. Pour in the chicken broth, add salt and black pepper. Stir to combine and let it simmer for a couple of minutes.
Now that the sausage has cooled down, cut it into slices that are 1/2 inch thick. Add them back into the skillet, cover with the sauce and let it them simmer for 5-7 minutes until the sauce has thickened and the sausages have cooked through.
Add in the cooked penne pasta, and combine to cover it with the sauce. Let it heat up for 1-2 minutes and remove from the heat. Garnish with green onion, basil, and parmesan cheese before serving.