Coat the bottom of a large soup pot with oil or cooking spray; heat over medium high heat.
Add the sausage and cook, stirring often and breaking apart sausage with a spoon, until well-browned (about 8 minutes). Remove sausage to a bowl.
Add onion and salt; cook, stirring often, until onion is softened (5-8 minutes).
Add garlic and red pepper flakes; cook, stirring, for 1 minute.
Add broth, turn heat up to high, and bring to a boil.
Add pasta and cook, stirring frequently, for 8 minutes.
Add broccoli and cook until pasta is al dente, about 4 minutes more.
Stir in cooked sausage, 3 tbsp Parmesan, lemon zest, and lemon juice; garnish with tomatoes, basil, and remaining Parmesan.
