Prepare the Filling:
In a large mixing bowl, combine the ground pork, cabbage, carrots, onion, garlic, soy sauce, oyster sauce (if using), black pepper, and beaten egg. Mix thoroughly until well combined.
Assemble the Lumpia:
Lay one lumpia wrapper on a clean surface with a corner pointing toward you (like a diamond).
Place about 2 tablespoons of the filling near the bottom corner of the wrapper, shaping it into a small log.
Fold the bottom corner over the filling, then fold in the sides, and roll tightly. Use a small amount of water to seal the edge of the wrapper. Repeat with the remaining wrappers and filling.
Fry the Lumpia:
Heat about 2 inches of vegetable oil in a deep frying pan over medium-high heat.
Once the oil is hot (350°F or 175°C), fry the lumpia in batches, turning occasionally, until golden brown and crispy, about 3–5 minutes.
Remove and drain on paper towels.
Serve:
Serve the lumpia warm with sweet chili sauce or your favorite dipping sauce.