For the short ribs: Whisk together the soy sauce, rice wine, brown sugar, sesame oil, gochujang and black pepper in a large bowl. Puree the garlic, onion, Asian pear and ginger in a food processor until smooth. Whisk into the soy mixture, then thin down with 1/3 cup water. Stir in the sesame seeds. Submerge the beef in the marinade and refrigerate for 2 hours or up to overnight, if time allows.
Remove the beef from the marinade and discard the marinade. Let the chill come off the beef for 30 minutes prior to grilling.
Preheat a grill or grill pan over high heat. Sprinkle the short ribs with salt and pepper and drizzle with olive oil. Place on the grill and cook until deeply charred on both sides, 1 to 1 1/2 minutes per side. Remove to a platter to rest while you make the salad.
For the banh mi salad: Whisk together the granulated sugar, rice vinegar, chile flakes and lime juice in a large bowl. Season well with salt and pepper, then add the cabbage, cilantro, mint and scallions, tossing to thoroughly coat.
Pile the salad up on one side of a platter. Shingle and stack the charred short ribs along the other side. Serve.