8 garlic cloves, peeled, crushed
1 2” piece ginger, peeled, sliced
1/2 cup dry sake
1/2 cup gochujang (Korean hot pepper paste)
1/2 cup mirin (sweet Japanese rice wine)
1/4 cup vegetable oil, plus more for grilling
1 1/2 pound skinless, boneless pork shoulder (Boston butt), sliced 3/4 thick
Purée garlic, ginger, sake, gochujang, mirin, and ¼ cup oil in a blender. Set ¼ cup marinade aside; chill. Transfer remaining marinade to a large dish. Add pork; turn to coat. Chill, turning occasionally, at least 2 hours.
Prepare grill for medium-high heat; oil grate. Remove pork from marinade and grill, basting with reserved marinade, turning occasionally, and moving pork to a cooler area if flare-up occurs, until cooked to desired doneness, 8–10 minutes for medium-rare.
Transfer pork to a cutting board and let rest 5 minutes before thinly slicing against the grain.
DO AHEAD: Pork can be marinated 1 day ahead. Keep chilled