Step 1: In a large skillet or wok, heat 1 tablespoon of vegetable oil over medium-high heat. Add the ground chicken and cook, breaking it up with a spoon, until it's no longer pink, about 5-7 minutes. Drain any excess fat.
Step 2: Add the diced onion and minced garlic to the skillet with the cooked chicken. Sauté for 2-3 minutes until fragrant and softened.
Step 3: Stir in the shredded cabbage and carrots. Cook, stirring occasionally, until the vegetables are tender-crisp, about 5-7 minutes. Add the bean sprouts and cook for an additional 2 minutes. Remove the skillet from heat.
Step 4: Season the filling by stirring in the soy sauce, oyster sauce, sesame oil, and black pepper. Taste and adjust seasonings as desired. Transfer the filling to a large bowl and let it cool completely to room temperature. This step is crucial to prevent soggy spring rolls.
Step 5: Thaw the spring roll wrappers according to package directions. Prepare a small bowl of water or a cornstarch slurry (1 tsp cornstarch mixed with 1 tbsp water) for sealing.
Step 6: Lay one spring roll wrapper on a clean, dry surface with a corner pointing towards you (diamond shape). Place about 2-3 tablespoons of the cooled filling near the bottom corner, shaping it into a log.
Step 7: Fold the bottom corner up over the filling, tucking it in snugly. Fold the left and right corners towards the center, like an envelope. Then, roll the spring roll tightly from the bottom up to the top corner. Dab the top corner with water or slurry to seal securely.
Step 8: Repeat the rolling process with the remaining wrappers and filling. Keep rolled spring rolls covered with a damp cloth to prevent drying.
Step 9: In a deep pot or Dutch oven, heat 2-3 inches of vegetable oil to 350°F (175°C). Do not overcrowd the pot; fry 3-4 spring rolls at a time.
Step 10: Carefully place the spring rolls into the hot oil. Fry for 5-7 minutes, turning occasionally, until they are golden brown and crispy on all sides. Ensure they are cooked through.
Step 11: Using tongs, transfer the fried chicken spring rolls to a wire rack lined with paper towels to drain excess oil. Serve immediately with your favorite dipping sauce.