Line a large tray or baking sheet with parchment paper. Separate the lumpia wrappers and keep them covered with a clean, barely damp kitchen towel so they stay flexible.
In a large bowl, combine the ground pork, carrot, onion, garlic, green onions, egg, soy sauce, salt, pepper, and cornstarch. Mix gently with clean hands or a fork just until evenly combined; do not overmix.
Place one wrapper on a clean work surface with one corner facing you. Add about 1 tablespoon of filling in a narrow line across the lower third of the wrapper, leaving about 1 inch (2.5 cm) clear on both sides.
Fold the bottom corner over the filling. Fold in the two side corners snugly, then roll upward into a thin cylinder. Dab the final corner with a little water and seal. Place seam-side down on the prepared tray. Repeat with the remaining wrappers and filling.
Pour oil into a deep skillet, Dutch oven, or wide saucepan to a depth of about 1 1/2 inches (4 cm). Heat over medium heat to 350°F (175°C). If you do not have a thermometer, a small piece of wrapper should sizzle steadily without browning immediately.
Fry the rolls in small batches, turning occasionally, until deep golden brown and the pork filling reaches 160°F (71°C) in the center of a roll. Keep the oil close to 350°F (175°C) between batches.
Transfer the fried lumpia to a paper towel-lined plate or a wire rack. Let them cool for a few minutes, then serve warm with sweet chili sauce, if desired.