Put olive oil in pot over medium heat. Once oil is hot, add onion, fennel, and salt. Cook uncovered for about 10 minutes, until onions and fennel are tender and jus starting to brown.
Stir in minced garlic and cook for another minute. Stir in the wine, vegetable broth, and red hot pepper flakes.
Add mussels to broth, cover, and cook over medium heat for about 10 minutes, until mussels are all opened. Discard any mussels that haven't opened during the cooking process.
Serve mussels in a bowl with broth poured over and parsley sprinkled on top.