Make the Vegetable Filling:

1. Heat oil in a large frying pan over medium-high heat for 2 minutes. Add ginger, garlic and mushrooms. Stir well for about 1 minute until fragrant. Add cabbage, carrots and green onions. Increase the heat to high and stir fry for about 2 minutes.
2. Add soy sauce, sesame oil, stock powder (optional), white pepper, and sugar. Stir well to combine, cover, and cook for 1 minute. (Note that cabbage contains lots of water and the vegetable mixture will start to get a bit soupy).
3. Remove the lid and turn the heat down to medium. Add cornstarch and stir well to combine. Cornstarch helps thicken the mixture. Add a little bit more if needed.
4. Allow filling to cool down completely before wrapping the spring rolls, about 10-15 minutes.

Wrap the Spring Rolls:

1. Place one spring roll wrapper diagonally (diamond shape) on a dry, clean flat surface. Keep the rest of the wrappers inside the package to prevent them from drying out.
2. Place  up to 1 and 1/2 tablespoons of vegetable filling in a horizontal line, 1/2-inch thick, placed approximately 1/4 of the way up from the bottom. Leaving about 2-inches uncovered on the side corners.
3. Fold up the bottom so that it covered the filling. The bottom corner should approximately touch the centre of the wrapper. Fold in the two side corners into the centre, folding over top.
4. Tightly roll the wrapper with your fingers until 1-2 inches remains on top. Lightly brush the remaining corner on top with water (or dip your finger into a bowl of water an apply it on the top corner). Roll up tightly to seal like a burrito. Make sure all corners are tightly sealed.
5. Place the top edge side down, and cover with a tea towel to prevent them from drying out.
6. Repeat steps with remaining spring rolls.

Deep Fry the Spring Rolls:

1. Add cooking oil into a medium sized pot and heat over high heat for 3 minutes, or until the oil starts shimmering and sizzling. The oil should be about 1/2-inch deep to just submerge the spring rolls.
2. Add in a batch of 4 spring rolls and cook for 2-3 minutes. Turn them over a few times so that both sides turn golden brown and cook evenly. Make sure the spring rolls are deep fried with some space in between each other.
3. Transfer the spring rolls onto a wire rack with a strainer and let it cool for at least 5 minutes before serving.
4. Repeat steps with remaining spring rolls. 

Make the Vinegar Dipping Sauce:

1. In a small bowl, combine black vinegar, sriracha (if using), and green onions. Stir with a spoon. 
2. Serve alongside the spring rolls, for dipping.