Bring a large pot of salted water (8 cups water, 1 tbsp salt) to a rolling boil. Add the dry pasta and cook according to package directions until al dente. Reserve 1 cup of the pasta cooking water before draining. Drain the pasta and set aside.

While the pasta cooks, heat 2 tbsp olive oil in a large skillet over medium heat. Add the finely diced onion and cook for 3-5 minutes until softened and translucent. Add the minced garlic and red pepper flakes (if using), and cook for another minute until fragrant, being careful not to burn the garlic.

Pour in 1/4 cup dry white wine or vegetable broth, scraping up any browned bits from the bottom of the pan. Let it simmer for 1-2 minutes until slightly reduced.

Reduce heat to low. Stir in 1/2 cup heavy cream, 2 tbsp fresh lemon juice, 1 tsp lemon zest, 1/2 tsp dried oregano, salt, and black pepper. Whisk gently until the sauce is smooth and heated through.

Gently flake the drained tuna into the sauce. Stir in 1/4 cup fresh chopped parsley and 2 tbsp fresh chopped chives.

Add the cooked and drained pasta directly to the skillet with the sauce. Toss everything together, adding a splash of the reserved pasta water as needed (1/4 to 1/2 cup) to reach your desired consistency. The pasta water helps the sauce cling to the pasta.

Remove from heat and stir in 1/4 cup grated Parmesan cheese until melted and incorporated. Taste and adjust seasoning if necessary.

Divide the creamy lemon herb tuna pasta among serving plates. Garnish with extra fresh parsley and lemon wedges if desired. Serve immediately.