Let's look over the ingredients:
1 pound dried fettuccine, spaghetti or linguine
1/2 cup extra virgin olive oil
2 large garlic cloves, or more to taste, finely minced
Generous pinch hot red pepper flakes
2 6-ounce cans tuna packed in olive oil, drained
Kosher salt
1/2 to 3/4 pound baby arugula
So, obviously baby arugula may not be something they're going to have at your local corner store. By the way, arugula is also known in Korea as rocket (로켓) or rucola (루콜라). You can identify it by its leaves:

It's not impossible to find in Korea, but spinach is probably an easier substitute. We usually make it with spinach and it's fine.
6 ounces is about 170 grams, FYI. A typical Korean can of tuna (참치) is going to be a little less than this (usually 150 grams). Speaking of which, you may be bedazzled and confused by the variety of canned tuna available to you here. I usually don't bother getting the olive oil tuna: I just drain the tuna, drench it in olive oil, then let it sit for a bit. The cheapest tuna is called "mild tuna" (마일드 참치):

By "mild" they mean "shredded finer and tastes somewhat blander than other sorts of canned tuna." I don't think it really matters in this dish, since you're adding garlic and hot pepper powder anyway. Do not fear the mild canned tuna.
For kosher salt, I use sea salt. You could just use regular salt, of course - not a big deal. Use it sparingly though - the hot pepper powder and the garlic add enough flavor to the dish.
Finally, I like to add button mushrooms. I slice them and sautee them first, by themselves, with a little olive oil and a sprinkle of rosemary. Then I take them out and add them later with the pasta and spinach.
You can eat it cold the next day, too. Yay for leftovers.