Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add breadcrumbs and toast until golden brown, stirring frequently to prevent burning. Transfer to a bowl and set aside.

Bring a large pot of salted water to a rolling boil over high heat. Add the pasta and cook, stirring occasionally, until it reaches an al dente texture, about 8 to 10 minutes. Before draining, reserve 1 cup of the pasta water. Drain the pasta thoroughly and set it aside for later use.

In the same skillet, warm the remaining olive oil over medium heat. Add the minced garlic and cook gently, stirring frequently, until the garlic releases its aroma and becomes translucent, about 1 minute. Be careful not to let the garlic brown, as this can impart a bitter taste to the dish.

Add the heavy cream to the pan, adjusting the heat to medium. Allow the cream to reach a gentle simmer, stirring occasionally. Continue cooking for 2-3 minutes, until the cream thickens slightly and coats the back of a spoon, ensuring it does not boil over.

Add the drained tuna to the skillet over medium heat, using a spoon to break it into smaller pieces. Stir gently to combine with the cream, ensuring the tuna is evenly distributed throughout the mixture. Cook for 3-4 minutes, allowing the tuna to warm through and absorb the flavors.

Transfer the cooked pasta into the skillet over medium heat, stirring gently to ensure it is evenly coated with the sauce. If the sauce appears too thick, slowly incorporate reserved pasta water, a tablespoon at a time, until the sauce reaches a smooth, creamy consistency that clings to the pasta.

Add the lemon zest and juice to the pan, stirring continuously over medium heat for about two minutes. This ensures the citrus aroma melds with the sauce, enhancing its brightness. Watch for the sauce to slightly thicken and become glossy, indicating the flavors are well combined and ready for the next step.

Sprinkle salt and black pepper over the pasta, adjusting to your preference. Toss the pasta continuously over medium heat until it is thoroughly coated, and the seasoning is well distributed. The pasta should be heated through, with a slight sheen, indicating the flavors have combined effectively.

Take the pan off the heat and evenly distribute the chopped parsley over the pasta. This adds a fresh, herbal aroma and a vibrant green color, enhancing the presentation. The parsley's subtle flavor will balance the richness of the dish, providing a refreshing contrast to the other ingredients.

Transfer the pasta to serving plates while still hot, ensuring even distribution. Sprinkle toasted breadcrumbs generously over the top, providing a satisfying crunch and a pleasing contrast to the creamy pasta. The breadcrumbs should be golden brown, adding a nutty aroma. Serve promptly to maintain the dish's warmth and texture.