Cherry tomatoes and a colorful combination of bell, sweet, and banana peppers are teamed with four pantry powerhouses to make a flavorful sauce for spaghetti: jarred tuna, golden raisins, Kalamata olives, and Parmesan cheese.
Heat a large straight-sided skillet or shallow pot over medium. Swirl in oil. Add onion, mild peppers, and 1 teaspoon salt. Cook, stirring occasionally, until vegetables have collapsed and are tender, 18 to 20 minutes. Add garlic, tomatoes, raisins, olives, and basil sprig. Cook, stirring occasionally, until tomatoes have collapsed and release their juices, and sauce thickens to a stew-like consistency, 6 to 8 minutes. Remove and discard basil.
Meanwhile, cook spaghetti in a large pot of generously salted boiling water until al dente, about 2 minutes less than package instructions. Reserve 1 cup pasta water, then drain. Transfer spaghetti and 1/2 cup pasta water to skillet with sauce and continue cooking, tossing a few times, until sauce thickens slightly and clings evenly to pasta, 3 to 4 minutes. Remove from heat. Add tuna, half of cheese, and finger pepper, tossing until evenly combined. Add more pasta water, a little at a time, until sauce evenly coats pasta again. Stir in basil leaves and serve, topped with remaining cheese and a drizzle of oil.