1. Heat a large deep skillet over medium high heat and add the olive oil. Add the sliced chicken apple sausage in a single layer and cook until browned on the first side, then flip and brown the other side. Transfer the sausage to a plate, leaving the flavorful oil and browned bits in the pan.

2. Reduce the heat to medium and add the chopped onion. Cook, stirring often, until the onion is soft and translucent, 4 to 5 minutes. Stir in the minced garlic and red pepper flakes and cook for 30 seconds, just until fragrant.

3. Pour in the chicken broth and water, scraping up any browned bits from the bottom of the skillet. Stir in the Italian seasoning, salt, black pepper, and Dijon mustard, and bring the mixture to a gentle simmer.

4. Add the dry pasta to the skillet, stirring so it is mostly submerged in the liquid. Cover the pan with a lid and cook at a steady simmer for about 8 to 10 minutes, stirring every few minutes so the pasta does not stick to the bottom.

5. Add the cherry tomatoes and return the browned sausage and any juices on the plate to the skillet. Continue to cook uncovered for another 3 to 5 minutes, stirring often, until the pasta is tender and most of the liquid has reduced into a starchy sauce. If the pan looks too dry before the pasta is cooked, add a splash of extra broth or water.

6. Lower the heat and pour in the heavy cream or half and half, stirring gently to combine. Let the sauce bubble for 1 to 2 minutes until slightly thickened, then turn off the heat and stir in the grated Parmesan cheese until melted and creamy. Taste and adjust seasoning with additional salt or pepper as needed.

7. Just before serving, sprinkle the pasta with chopped fresh basil or parsley and the lemon zest if using. Toss gently to combine, then serve hot with extra Parmesan on top.