Bring a large pot of salted water to a rolling boil. Add the pasta and cook according to package directions until al dente. Before draining, reserve about 1 cup of the starchy pasta water. Drain the pasta and set aside.

While the pasta is cooking, heat the olive oil in a large skillet or pan over medium heat. Add the finely diced onion and cook, stirring occasionally, until softened and translucent, about 5-7 minutes.

Add the minced garlic and red pepper flakes (if using) to the skillet. Cook for another minute until fragrant, being careful not to burn the garlic.

Stir in the drained tuna, lemon zest, and fresh lemon juice. Break up the tuna gently with a spoon. Cook for 1-2 minutes to allow the flavors to meld.

Pour in the heavy cream and 1/4 cup of the reserved pasta water. Bring the sauce to a gentle simmer and let it cook for 2-3 minutes, stirring occasionally, until it slightly thickens. Season generously with salt and black pepper to taste.

Add the drained pasta directly to the skillet with the sauce. Toss well to coat the pasta evenly. If the sauce appears too thick or dry, add more reserved pasta water, one tablespoon at a time, until you reach your desired creamy consistency.

Remove the skillet from the heat. Stir in the chopped fresh parsley and fresh dill (or basil). Give it one final toss.

Serve the creamy lemon herb tuna pasta immediately, garnished with extra fresh herbs and a sprinkle of grated Parmesan cheese, if desired. Enjoy your delicious tuna pasta!