Bring a large pot of salted water to a boil. Add the pasta and cook according to the package instructions until al dente. Before draining, reserve ½ cup of pasta cooking water, then drain the pasta.

While the pasta cooks, melt the butter in a large skillet over medium heat. Add the minced garlic and sauté for about 30 seconds until fragrant, stirring frequently to prevent it from burning.

Add the sliced mushrooms and cook for 4–6 minutes, stirring occasionally, until tender and golden brown. Allow any excess moisture to evaporate so the mushrooms develop a rich, savory flavor.

Stir in the tomato paste and cook for about a minute. Pour in the heavy cream and stir until the sauce is smooth. Let it simmer gently for 2–3 minutes until slightly thickened.

Add the drained tuna and gently break it into smaller pieces with a spoon. Stir it into the creamy mushroom sauce and cook for another 1–2 minutes. Season with salt and freshly ground black pepper to taste.

Add the cooked pasta to the skillet and toss until evenly coated in the sauce. Gradually stir in a little reserved pasta water as needed to loosen the sauce and help it cling to the pasta.

Stir in the chopped parsley, lemon juice, and grated Parmesan, if using. Taste and adjust the seasoning as needed. Serve immediately with extra parsley, freshly cracked black pepper, and additional Parmesan if desired.