Heat the olive oil in a large frying panover medium heat. While the oil is still not hot yet, add the garlic to start infusing. Make sure to coat the garlic with oil.
When the garlic is sizzling and well-coated with oil, add the cabbage and coat with the oil.
Add the canned tuna and toss together with the cabbage. Then add freshly ground black pepper, unsalted butter, and miso.
Reserve ¼ cup of pasta water and add to the pan. Shake the pan and mix all the ingredients together. Make sure the miso is dissolved while mixing.
Add the soy sauce and mirin.
When the spaghetti is done cooking, pick up the spaghetti with a pair of tongs (or you can quickly drain in the sink) and add to the pan. Toss the spaghetti to mix all together.
Season the spaghetti with freshly ground pepper. Taste and add salt if needed. The reserved pasta water I added has enough salt so I do not add additional salt here. Serve the pasta to individual dishes. Enjoy!