1. In a medium bowl, stir together the garlic, gochujang, mirin, soy sauce, ginger and sesame oil. Add the pork and let marinate at room temperature for about 30 minutes, or cover and refrigerate up to overnight. Preheat the oven to 95°C
2. Heat a large skillet or frying pan over medium-high heat. Spread the cut sides of the rolls with the butter. Working in batches if needed, toast the rolls, cut-side down, until lightly golden, gently pressing on them so the centers toast, about 1 minute. Transfer the rolls to the oven to keep warm.
3. Wipe out the skillet and return it to the stove. Add the vegetable oil and heat over medium-high heat. Add the marinated pork and cook, stirring occasionally, until the meat is cooked through and golden and lightly charred in spots, about 5 minutes. Add the onions, mushrooms and chiles and cook, stirring occasionally, until the onions and mushrooms have softened slightly, about 2 minutes. Divide the mixture into two mounds in the skillet and top each mound with half of the cheese. Cover the skillet and cook just until the cheese melts, about 1 minute.
To serve: Scoop each mound onto a roll and sprinkle with some scallions, sesame seeds, gochugaru and pickled jalapenos. Serve immediately.
Cook's Note: These cheesesteaks were the biggest hit when we were filming. They didn't last one minute after the camera stopped rolling.