Heat a wok over a high heat, add 2 tablespoons of the oil, give the oil a swirl and then cook the garlic and ginger, tossing for a few seconds. Add the fresh shiitake mushrooms and cook for a few minutes until they start to soften. Add the Chinese five-spice powder and toss well. Add the vegetable mixture and oyster sauce and toss well, cooking for less than 1 minute. Add the sriracha and soy sauce to taste, toss well and transfer to a plate to cool.
Reheat the wok over moderate heat and add the remaining quart peanut oil to fry the egg rolls.
To assemble the egg rolls, place a spring roll wrapper on a flat surface with a corner pointed toward you and top with a second spring roll wrapper, lining up edges. Spoon about three tablespoons of the filling across the middle of the wrappers.
With a pastry brush, brush the wrapper edges lightly with the beaten egg (this helps the egg rolls from bursting open while frying). Fold in the side corners of the wrappers toward the middle, fold up the bottom corner and then roll into a cigar shape. Press gently to seal. Repeat with the remaining 6 wrappers and filling to form 4 rolls total.