Bring a large pot of salted water to a boil. Add spaghetti and cook until al dente, about 8-10 minutes. Drain and return to pot, drizzling with olive oil.

In a skillet, heat olive oil over medium heat. Add red onion and sea salt, sautéing for 3-5 minutes. Add garlic, stirring for another 30 seconds.

Gently add sardines, breaking into chunks and stirring to combine with onion and garlic for about 2 minutes.

Add the cooked spaghetti, tossing it with the sardine mixture to coat well.

Squeeze lemon juice over pasta and add zest. Toss in arugula and grated cheese, adjusting salt and pepper to taste.

Transfer to serving plates and sprinkle with panko breadcrumbs. Serve hot.