Place the beef in a bowl. Pour in the soy sauce. Add the pepper and garlic. Mix well. Cover and leave to marinate in the fridge for a couple of hours.
Heat a large wok or frying pan. Coat the bottom generously with cooking oil.
Drain the beef.
When the oil is hot, throw in the beef and pan fry over very high heat just until the meat is cooked through. Do not overcook as beef turns tough and rubbery when overdone. Scoop the meat out of the pan and transfer to a serving platter.
In the remaining oil and juices, cook the onion rings just until softened.
Top the beef with the onion rings.
Pour the kalamansi juice into the pan, scraping whatever bits and remaining juices there there.
Pour the contents of the pan over the meat and onions. Sprinkle the bistek with sliced scallions and serve hot with rice.