Add the sesame oil to a large skillet over medium-high heat. Once the oil is hot & shimmering, add the ground pork & brown for 5-6 minutes. As the pork cooks, season with oyster sauce, soy sauce, salt, white pepper, & garlic powder, & use a wooden spoon to break it apart into fine pieces.
Once the pork is cooked through, add in all the vegetables. Stir to combine with the pork, then stir fry 3-4 minutes, until softened slightly. Remove the skillet from the heat & transfer the pork egg roll filling to a large bowl. Set aside to cool for egg roll assembly.
Line a quarter sheet pan with wax paper or parchment paper & set aside. Fill a small bowl with water. Place the pork egg roll filling, egg roll wrappers, & water within arm's reach of where you plan to assemble the egg rolls.
Place an egg roll wrapper on a work surface in front of you with one point pointing toward you, orienting it in a diamond shape. Spoon about ⅓ cup of the pork egg roll filling on the center of the wrapper. Fold the point closest to you away, to fold over the egg roll filling. Fold the points to the left & right of the filling to the center. Roll the filling away from you towards the last point, creating an egg roll. Use your fingertips to brush a little water over the last point, then press it against the egg roll to seal.
Add frying oil to a small skillet, filling it about halfway full. Preheat over medium-high heat, until the oil is hot. Working in batches, carefully place the egg rolls in the oil. Cook until the bottom of the egg roll is golden, then flip & cook until the entire egg roll is golden & crisp. Carefully transfer to a paper towel-lined Repeat frying until all egg rolls are cooked, allowing the oil to come back up to temperature between batches.