Heat a pan over medium heat and add the oil for stir-frying. Add the sliced onion and sauté until fragrant. Add the shredded carrot, king oyster mushrooms, and diced hot dogs. Stir-fry until well combined.

Add the oyster sauce and seasoning powder. Stir-fry until everything is cooked through, then turn off the heat. Transfer the filling to a bowl and let it cool.

To assemble, take out one spring roll wrapper at a time. Place some filling in the center, then sprinkle mozzarella cheese on top as desired.

Wrap the spring roll as shown in the picture.

To fry, heat a pan or pot with the oil for frying over high heat. Once the oil is hot, add the spring rolls. Immediately reduce to medium heat. When the spring rolls start to turn golden, switch back to high heat briefly so they don't absorb too much oil. Quickly remove the spring rolls and place them on a tray lined with paper towels to drain excess oil. (Don't fry too long since the filling is already cooked.)

Slice the spring rolls as you like. You can enjoy them as is, since they're already flavorful, or serve with dipping sauce if you prefer.