Add the butter to a nonstick skillet and melt it over medium-low heat. Cut the bottoms off the tomatoes and place them cut-side down on the left side of the pan. Add the bacon to the center of the pan, then place the chopped onion on the right side. Add the minced garlic.
Cook over medium heat for about 1 minute, or until the bottom side of the bacon starts to brown.
Flip the bacon, then place the pasta directly on top of the bacon. Add the slices mushrooms on the onions. In a small bowl, combine the heavy cream, stock, gochujang, mayo, ketchup, and soy sauce. Stir until smooth. (In the video, I added the seasonings separately directly into the pan for a more visually satisfying presentation, but for the best and most even flavor, it’s recommended to mix the sauce together beforehand.)
Pour the sauce mixture into the pan. Cover with a lid and cook for 5 minutes.
Open the lid and remove the tomato peels. Use a potato masher to crush the tomatoes directly in the pan, then cut the bacon into bite-sized pieces. Stir everything well to combine, then cover again and continue cooking until the spaghetti is al dente.
If the liquid reduces too quickly before the pasta is fully cooked, add a little water as needed.
Once the pasta is cooked, remove the lid. Add the gouda cheese and stir everything together until the sauce becomes creamy and thickened.
Plate the pasta and optionally sprinkle dried parsley on top for garnish before serving.