Begin by bringing a large pot of salted water to a boil. Add the spaghetti and cook until al dente, following the package instructions. Once done, drain and drizzle with a little vegetable oil to prevent sticking.

In a large skillet, heat 2 tablespoons of vegetable oil over medium heat. Add the chopped onion and cook until it becomes soft and translucent, about 5 minutes.

Stir in the minced garlic and half of the freshly chopped parsley. Allow it to cook for about 1 minute until fragrant.

Toss in the diced tomato and cook for 3 to 5 minutes, letting it soften and release its juices.

Add the drained tuna into the skillet, breaking it apart gently while mixing it well with the other ingredients.

Sprinkle in salt, pepper, and chili flakes to taste. Allow it to simmer for about 2 to 3 minutes for all the flavors to meld together.

Add the cooked spaghetti to the skillet and toss everything together until well coated.

Sprinkle the grated cheese on top and toss until it melts into the spaghetti. Finish by adding the remaining parsley for an extra burst of freshness.

Plate the delicious tuna spaghetti and serve immediately.