Bring 3 litres of water to a boil in a large pot or Dutch oven and season with 1 tablespoon of salt.
Cook the pasta. Set your timer for 3 minutes shy of what the package says is the cooking time.
While the pasta cooks, prepare your fresh green beans by removing the stem end and cutting them into 1-inch lengths. Set the green beans aside.
Zest the lemon and set it aside, and open and drain the can of tuna.
3 minutes before the pasta finishes cooking, add the trimmed green beans to the pot and allow to cook for the remaining minutes.
Drain the pasta and the green beans through a strainer and set aside. Save some of the pasta water in case you need it for the sauce.
Return the pot to the stove and add the olive oil.
Grate in the garlic, then immediately add the tuna so the garlic doesn’t burn
Add the tomato sauce and the sour cream, then add the pasta and green beans and stir to combine.
Sprinkle in the parsley, the lemon zest, and the juice of half the lemon, and stir.
Finish with a squeeze of additional lemon juice, some shredded parmesan cheese, and a sprinkle of red pepper flakes (optional).