Pour the olive oil into a saucepan over medium-high heat and add the fennel seeds to roast them. Add the chopped red onion. Season with salt and pepper.
Remove the casings from the sausages and add the meat to the pan. Sauté for about 5 minutes, breaking it up with a spoon.
Dice the celery, fennel and leek. Add the vegetables to the sausage mixture. Save the celery leaves and fennel stalks for serving.
Add the garlic, herbes de Provence, chili flakes and bay leaves. Continue cooking for about one minute, stirring regularly. Season with salt and pepper to taste.
Add the rice and chicken broth, then stir. Bring to a boil and simmer over medium-low heat for about 45 minutes.
Add the Italian parsley and oregano, then stir. Adjust seasoning to taste and add about 2 tbsp of lemon juice.
Serve in bowls and garnish with lemon zest, a few celery leaves, fresh fennel stalks and a dash of crushed chili flakes.