Cook the Spaghetti: Boil water in a large pot and cook the spaghetti according to package directions until just tender. Drain, reserving about 1/4 cup of the pasta water for later use.
Prepare the Bread Crumbs: In a skillet, heat 2 tbsp olive oil over medium heat. Add the bread crumbs to the hot oil and stir frequently until golden brown and fragrant (about 3-4 minutes). Once done, transfer the bread crumbs to a plate and set aside.
Cook the Sardine Mixture: Add the remaining 2 tbsp olive oil to the same skillet. Add the chopped onion and season with a pinch of salt and pepper. Stir occasionally until the onion becomes soft and translucent, about 5-6 minutes.
Flavor the Dish: Increase the heat to medium-high. Add the zest and juice of 1/2 lemon, the capers (if using), and the thoroughly drained sardines to the skillet. Stir to combine and cook for 2-3 minutes until heated through.
Combine Pasta and Sardine Mixture: Add the drained pasta to the skillet and toss well, ensuring the pasta is coated with the sardine mixture. If needed, add some reserved pasta water to help moisten the dish.
Finish the Dish: Stir in the bread crumbs and parmesan cheese until evenly combined. Taste and adjust seasoning as desired.
Notes
No Sardines: The best nutrient equivalence is herring, mackerel, or salmon, but you could also use shrimp.
Leftovers: Store in airtight container in the refrigerator for up to 3 days.
