To make the sauce, whisk together the gochujang, low-sodium soy sauce, sesame seeds, vegetarian oyster sauce, sesame oil, water, and gochugaru in a small bowl and set aside.

Melt 2 tablespoons of the butter in a large sauté pan over medium high heat. Once the butter is melted, add the mushrooms and crumble in the tofu with your hands. Season with the dark soy sauce and cook, mixing every couple of minutes, until the moisture has cooked out of the mushrooms and the tofu starts to crisp on the outer edges, 8 to 10 minutes. Remove the mushrooms and tofu from the pan and set aside.

In the same pan, melt the remaining 2 tablespoons of butter over medium heat. Once the butter is melted, add the white parts of the green onion and garlic, and cook, mixing often, until the onions become translucent and the garlic is fragrant, 5 to 6 minutes. Reduce the heat to medium low. Pour in the sauce, add the noodles and the broth and simmer, mixing to combine, until the noodles are cooked through. Add the tofu and mushrooms back into pan and mix again to combine. Serve with sesame seeds and fresh green onion, and enjoy!