Heat the olive oil and butter in a frypan over high heat. Season the pork chops with salt and pepper then place in the frypan in the hot oil; cook until browned on both sides, about 3 minutes per side. Reduce heat to medium and continue cooking until the pork is no longer pink in the center, about 6 minutes more.
Remove pork chops from the frypan and set aside. Add the sliced onion to the frypan; cook and stir until the onion has softened and turned translucent, about 5 minutes. Stir in the lemon juice and soju, scraping up any brown bits from the bottom of the frypan. Simmer until liquid as reduced, about 2 minutes. Season with salt and pepper, and drizzle the sauce over the pork chops for serving.