Begin by thoroughly cleaning the milkfish—gut it while leaving the scales on to help preserve the texture during simmering. Once cleaned, portion the fish into individual servings.
In a wide, shallow pot, layer the fish, eggplant wedges, thin onion slices, crushed garlic, and pounded ginger. Pour in the vinegar and water, ensuring the ingredients are partially submerged. Add the finger chili peppers for subtle heat, then sprinkle in the salt and whole peppercorns to deepen the flavor.
Cover the pot and let the mixture simmer over medium heat for 10 to 15 minutes. The stew is ready once the fish is fully cooked and the liquid has reduced to a savory, slightly tangy broth.
To finish, drizzle canola oil over the dish and gently stir to blend the flavors without breaking apart the tender fish. Serve piping hot for a comforting, bold-flavored Filipino stew.