In a bowl, combine pork, calamansi or lemon juice, soy sauce, onions, garlic, and pepper. Massage the marinade into the meat and marinate for about 30 minutes.
Drain meat, onions, and garlic from marinade, squeezing and reserving excess liquid. Set aside.
In a pan over medium-high heat, heat 2 tablespoons of the oil. Add pork chops and cook for about 2 to 4 minutes per side or until lightly browned. Spoon out and reserve released meat juices during frying. Remove meat from pan and keep warm.
In the pan, add the remaining 1 tablespoon oil. Add the reserved onions and garlic, and cook, stirring regularly, until softened.
Return meat to pan.
Add reserved marinade and meat juices.
Add water and bring to a boil, skimming scum that floats on top.
Cover, lower heat and simmer for about 40 to 50 minutes or until meat is fork-tender and liquid is reduced.
Season with salt to taste.
Add the onion rings. Turn off heat, cover and allow onion slices to cook slightly in the steam. Serve hot.