Boil pasta in salted water al dente.
Peel onions and garlic and chop finely. Drain sardines in a sieve. Wash zucchini and grate coarsely.
Drain the pasta. Heat the oil in the pasta pot and fry onion and garlic briefly. Add rosemary and towelled lemon zest and sauté briefly. Season with salt and pepper.
Pour in the juice of the lemon. Place noodles back into the pot, mix well and reheat. Fold in half of the sardines and season with salt and pepper.
To serve, spread the remaining sardines and Zucchini zests.