In a saucepan over medium heat, warm olive oil. Add fennel bulb, fronds, and onion; sauté until tender, around 5 minutes. Mix in garlic and cook for another minute. Add sardines with oil, breaking them apart while stirring. Incorporate raisins, pine nuts, basil, fennel seeds, salt, pepper, and red pepper flakes; cook until fragrant. Pour in tomatoes and let the sauce simmer.
Boil a large pot of salted water. Cook spaghetti until al dente, about 12 minutes, stirring occasionally.
In a separate pan, warm oil over medium heat. Sauté garlic until fragrant, approximately 1 minute. Mix in bread crumbs and basil. Cook until golden brown, stirring occasionally for about 3 minutes. Take off the heat.
After draining the pasta, serve it topped with the sauce, seasoned bread crumbs, and Parmesan cheese.