Boil a large amount of salted water in a pot. Once it comes to a boil, boil the pasta (according to the package directions).
While the pasta boils, melt the butter in a frying pan and add the onions cut into easy-to-eat pieces, bacon, and mushrooms and stir-fry.
Once cooked through, add the Korean dashida and grainy mustard. Add the boiled pasta and toss to coat. Turn off the heat. Add the arugula and transfer to a plate.
Sprinkle a generous amount of black pepper and serve. My husband loves it with grated cheese on top. Make it as you like.