Bring a large stock pot of water to a boil and season generously with kosher salt. Add the spaghetti and cook until al dente, about 10 minutes.
While the pasta is cooking, add the tuna, olive oil, lemon zest and juice, salt, red pepper flakes, and capers to a large bowl. Drain the pasta once it’s ready and add to the bowl, tossing everything together with tongs. Then add the arugula (you want to toss the pasta a few times before adding the greens so they wilt without getting soggy). Taste and add more salt or red pepper flakes if desired. To serve, top with parsley or dill and some grinds of black pepper.
Notes
Feel free to add a small clove of grated garlic if you love garlic Olives could be a nice addition to this pasta Use anchovies instead of tuna Add some chopped roasted red peppers or sun-dried tomatoes