2 tbsp peanut oil or vegetable oil, plus extra for deep-frying
4 scallions, cut into 2-inch/5-cm lengths and shredded lengthwise, plus extra to garnish
1 -inch/2.5-cm piece fresh ginger, peeled and finely chopped
1 large carrot, peeled and cut into thin sticks
1 red bell pepper, seeded and cut into thin sticks
6 tbsp black bean sauce
1/3 cup fresh bean sprouts
7 oz/200g canned water chestnuts, dried and coarsely chopped
2 -inch/5-cm piece cucumber, cut into thin sticks
Eight 8-inch/20-cm square egg roll skins
Sweet chili dipping sauce, to serve (optional)