Bring a large pot of lightly salted water to a boil. Add spaghetti and cook until al dente, 8 to 10 minutes. Drain and rinse under cold water. Toss with ¼ cup olive oil; cover and keep warm.
Place ¼ cup olive oil in a skillet over medium heat. Stir in garlic; cook just until golden, 2 to 3 minutes. Add sardines; cook 1 minute more. Stir in bread crumbs and ⅓ cup Parmesan cheese. Stir in remaining ¼ cup olive oil if necessary to give mixture a crumbly texture. Stir in parsley and pepper and remove from heat.
Serve sardine mixture over spaghetti and garnish with additional Parmesan cheese.
