Marinate beef in kalamansi juice, soy sauce, salt and pepper for 30 minutes to an hour.

Pan fry the marinated beef slices in hot oil, until cook. Transfer to a serving plate.

Sauté the onions from the same pan with the remaining oil and cook until tender but firm. Set aside.

Using the same pan, pour in the excess marinating liquid and heat up for a few minutes then thicken with cornstarch that has been diluted to water.

Once thickened, Pour the sauce over to cooked beef slices and arrange or garnish on top sautéed onion rings.