Prepare String Beans: Coat string beans with oil and salt, then arrange in a single layer.
Broil String Beans: Broil string beans for about 5 minutes until slightly charred.
Cook Aromatics: In a hot pan, add oil, Sichuan peppercorns, and ground pork. Cook until pork is browned.
Add Aromatics: Add garlic, ginger, and preserved mustard greens, stirring to combine.
Combine with String Beans: Add broiled string beans, salt, sugar, and MSG. Stir fry for another 15 seconds.
Finish with Scallions: Add scallions and toss everything together for a final minute.
Serve: Plate the dry fried string beans and serve immediately.