Heat the olive oil in a large saucepan. Add the onion and cook over moderate heat until softened but not browned, about 5 minutes. Add the garlic and cook until fragrant, about 1 minute.
Wrap the coriander seeds and bay leaves in cheesecloth and tie with string.
Stir the herb bundle into the saucepan along with the wine, stock, sugar and cayenne and bring to a boil. Reduce the heat, cover and simmer gently for 10 minutes.
Add the fennel, carrots and a little salt to the saucepan and simmer over moderate heat until almost tender, about 10 minutes.
Add the zucchini and bell pepper and simmer until all the vegetables are tender, about 10 minutes. Using a slotted spoon, transfer the vegetables to a bowl.
Boil the cooking liquid until flavorful and slightly thickened, about 10 minutes. Discard herb bundle.
Remove the pan from the heat and let the cooking liquid cool to lukewarm, then stir in the hazelnut oil. Season with salt; add more cayenne or hazelnut oil if needed.
Pour the cooking liquid over the vegetables, scatter the watercress sprigs sparingly over the top and serve warm or at room temperature.