If using, cut a small hole in the center of each piece of beef and add a strip of pork fat.
Place the prepared beef in a large bowl and add the soy sauce, calamansi juice, and a sprinkling of freshly ground black pepper. Toss to coat, then cover and refrigerate for 1-3 hours.
In a large pot, drizzle the oil over medium heat.
Once hot, add the onions and cook, stirring occasionally, until softened.
Add the garlic and cook until just fragrant, 30 seconds to 1 minute.
Remove the beef from the marinade (reserve the liquid) and add to the pot. Cook, stirring occasionally, until browned on all sides.
Add the water, tomato sauce, reserved marinade, bay leaves, salt, and pepper. Stir to combine and bring the mixture to a boil.
Reduce heat to a simmer, cover, and cook over low heat for 1 1/2 hours, until the beef is tender.
Add the potato, carrot, and bell pepper pieces. Continue to cook for another 20-30 minutes, until the vegetables are tender.
Season with salt and pepper to taste.
Serve hot with steamed rice.