Heat oil in a large stockpot over medium-high heat until shimmering. Add onion and sausage and cook for 5-7 minutes until the onion is translucent and the sausage begins to slightly brown, stirring occasionally. Add garlic and cook for an additional 1-2 minutes until fragrant. Add chicken broth, sweet potatoes, and tomatoes and stir to combine. Bring to a boil, then reduce heat to medium-low, cover, and let simmer for 5 minutes. Add the pasta, stir to combine, and let cook for an additional 10-15 minutes or until the pasta is al dente. Stir in the kale, and season the soup with black pepper and additional salt if needed. Serve warm garnished with lots of freshly-grated Parmesan cheese.