Blend all the ingredients for chimichurri sauce together till fairly smooth in a blender or food processor. Remove to a clean jar and set aside. This can be refrigerated for up to 3 days.Cook the pasta in a large pot of salted boiling water till al-dente, 12-13 minutes. Drain and set aside.Meanwhile, heat a large skillet and add the sausage slices. Brown them on both sides and remove to a plate.There should be rendered fat left in the skillet. If not, add 1 tbsp of olive oil. Add the chicken and mushroom and season with black pepper powder and salt. Cook on all sides till chicken is opaque, 5-6 minutes.Return sausages to pan. Add pasta and ½ cup of chimichurri sauce. Toss to coat everything well with the sauce. You can add more sauce if needed, or reserve it for future use.Serve warm with or without cheese.