Soak the shiitake mushrooms in a bowl of cold water for 20-30 minutes (or even overnight in the fridge if you have the time).
Prepare the vegetables for the filling by shredding the cabbage and carrots, dicing the shiitake mushrooms and green onions, and grating the ginger.
Add the pork, sesame oil, mirin, soy sauce, ginger, green onions, salt, and pepper to a large skillet and cook on medium-high heat until the pork is beginning to brown (about 3 minutes).
After 3 minutes of so, add shredded cabbage, carrots, shiitake mushrooms, bamboo shoots, and chicken stock to the pork mixture and cook for around five minutes (or until the vegetables are fully cooked).
Once the veggies are cooked, remove the mixture from heat and allow to cool to room temperature.
Heat the vegetable oil in a sauce pan on medium heat until the temperature is around 350 degrees.
Once the filling mixture is cool, evenly divide the filling into ten servings.
Place one serving of mixture in one corner of the spring roll wrapper. Starting with the corner that contains the filling, roll wrapper over the filling until you reach the halfway point.
Once you are halfway through wrapping the harumaki, wet the unrolled sides of the spring roll wrapper, fold in the two side corners, and continue wrapping the roll until it's fully wrapped. While wrapping the last half of the roll, use your fingers to ensure you have a small air pocket to prevent the roll from popping when cooking.
Cook the harumaki in the oil for around 3 minutes, or until the wrappers are crunchy and light brown in color.
Serve and enjoy!