In Sicily, pasta con le sarde (with sardines and wild fennel) is the traditional preparation for the hollow spaghetti known as bucatini. This is a simple and satisfying dish, and the only trick is timing it right so that the sardines are ready just as the pasta approaches al dente.
In a small pan, heat the reserved oil from the can of sardines. When hot, add the breadcrumbs and cook, stirring, until they have toasted to a deep brown. Remove the pan from the heat and mix in the lemon zest. Set aside.
Begin to cook the bucatini in a large pot of boiling salted water. Note that you will need to remove it from the pot before it is fully cooked.
Place the olive oil and sliced garlic in a large cold skillet and turn the heat to medium. Cook, stirring frequently, until the garlic is golden (but not browned). Remove the garlic from the pan and set aside.
Add the fennel and hot pepper flakes to the pan and cook for 5 minutes, until softened. Add the sardines, breaking them up with a wooden spoon. Add the lemon juice and stir to combine.
When it is just shy of al dente, remove the pasta from the water and add it to the large pan with the fennel and sardines, along with a ladle of pasta water. Turn the heat up to high and stir to combine. Cook until the pasta reaches the desired doneness, adding more pasta water as needed. Once perfectly done, add the breadcrumbs and garlic and toss to combine. Serve immediately in warm bowls.