Prepare the Lumpia Filling: In a large mixing bowl, combine the ground pork, finely chopped shrimp (if using), diced carrots, diced water chestnuts, sliced green onions, and minced garlic. Ensure all ingredients are evenly distributed.

Add the flavorings to the filling mixture: Pour in the soy sauce and oyster sauce (if using). Season generously with freshly ground black pepper. Mix everything thoroughly until well combined. It helps to use your hands for this step to ensure even distribution of seasonings.

Bind the filling: Add the lightly beaten egg to the mixture. Mix again until the egg is fully incorporated, acting as a binder for all the ingredients.

Assemble the Lumpia: Lay one lumpia wrapper flat on a clean, dry surface with one corner pointing towards you (diamond shape). Place about 1 to 1.5 tablespoons of the filling mixture near the bottom corner of the wrapper, shaping it into a thin log.

Fold the bottom corner of the wrapper tightly over the filling. Fold in the left and right sides of the wrapper towards the center, creating a neat envelope shape. Moisten the top corner of the wrapper with a little water using your finger or a pastry brush.

Roll the lumpia tightly from the bottom corner upwards to seal. Ensure there are no gaps to prevent oil from seeping into the filling during frying. Repeat this process with the remaining filling and wrappers until all lumpia are formed. Place the finished lumpia on a plate or baking sheet, seam-side down.

Prepare for Frying: Pour the vegetable oil into a deep pot or wok, ensuring it's at least 5-7.5cm (2-3 inches) deep. Heat the oil over medium-high heat until it reaches 175°C (350°F). You can test the oil temperature by dropping a small piece of wrapper; it should sizzle immediately and float to the surface.

Fry the Lumpia: Carefully place 5-7 lumpia into the hot oil, being careful not to overcrowd the pot. Overcrowding will lower the oil temperature and result in soggy lumpia. Fry for about 4-6 minutes, turning them occasionally with tongs, until they are golden brown and crispy on all sides.

Drain the Lumpia: Once golden and crispy, remove the lumpia from the hot oil using a slotted spoon or spider strainer. Place them on a wire rack set over a baking sheet to drain any excess oil. This helps maintain their crispiness.

Repeat the frying process with the remaining lumpia, ensuring the oil temperature returns to 175°C (350°F) between batches. Adjust the heat as needed.

Serve: Arrange the hot, crispy lumpia on a serving platter. Serve immediately with sweet chili sauce for dipping. Garnish with lime wedges if desired.