Filipino-style Beef Steak (Bistek)

1-1/2 lbs (750 g) beef sirloin or skirt steak, cut into thin fillets 
2 tablespoons kalamansi lime juice or lemon juice 
2 tablespoons soy sauce 
2 teaspoons freshly ground black pepper 
3 tablespoons oil 
1 medium onion, sliced into rings 
Salt to taste

1 Marinate the beef slices in the kalamansi lime juice, soy sauce and pepper overnight in the refrigerator. 
2 Heat the oil in a skillet and pan-fry the beef until medium-rare, about 30 seconds on each side. Transfer the beef slices to a plate. 
3 In the remaining oil, stir-fry the onion until it is browned. Season the beef with a sprinkling of salt and drizzle a little of the pan juice over the steak. Garnish with the onion slices and serve. 

Serves 4 
Preparation time: 10 mins + overnight marination 
Cooking time: 10 mins