Bring a large pot of salted water to a boil.

Add spaghetti and cook according to package directions until al dente.

While the pasta is cooking, prepare the other ingredients.

Drain the pasta and return it to the pot.

Stir in butter, olive oil, salt, and pepper.

Add flaked tuna (undrained), diced pimiento (or sliced roasted red peppers), sliced green onions, sliced black olives, chopped walnuts, and shredded Swiss cheese.

Toss all ingredients together until well combined.

Serve immediately, garnished with fresh parsley or cilantro.