Korean spicy marinated pork (dae ji bool gogi)

Name: Korean spicy marinated pork (dae ji bool gogi)
Prep time: 45 min
Cook time: 15 min
Total time: 1 h
Cuisine: Asian, Korean
Ingredients: 4 tablespoons rice wine vinegar; 2 tablespoons soy sauce; 8 tablespoons gochujang (Korean chilli paste); 3 tablespoons minced garlic; 3 tablespoons minced fresh ginger; 2 tablespoons red chilli flakes; 1/2 teaspoon black pepper; 3 tablespoons caster sugar; 3 spring onions, cut into 5cm pieces; 1/2 onion, cut into 6mm thick rings; 900g pork fillet, cut into 6mm slices; 4 tablespoons rapeseed oil