In a large pot or Dutch oven, heat the vegetable oil over medium heat.
Add the diced pork and cook until browned on all sides. Remove the pork from the pot and set aside.
In the same pot, add the chopped onion, minced garlic, and minced ginger. Cook until the onion is translucent and fragrant.
Stir in the soy sauce, oyster sauce, and tomato paste. Cook for another minute, allowing the flavors to blend.
Return the browned pork to the pot. Add the water, brown sugar, black pepper, salt, and bay leaves. Stir to combine.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 1 to 1.5 hours, or until the pork is tender and the flavors have melded together.
If you prefer a thicker sauce, mix the cornstarch with a little water to form a slurry, then stir it into the pot. Cook for an additional 5 minutes, until the sauce has thickened.
Remove the bay leaves. Serve the Keke Pua'a over cooked rice.
Enjoy your meal!