Preheat oven to 400ºF with rack in the center.
Heat canola oil in a large, nonstick skillet over high heat. Add pork and brown for 2-3 minutes, breaking it up into small pieces with a wooden spoon. Add the celery and mushrooms, stir-fry for 1 minute, then add the cabbage, bean sprouts, water chestnuts, garlic and ginger, and cook 2-3 minutes more.
Stir in the tamari, then transfer the egg roll filling to a bowl and let cool. Once cool enough to handle, mix in the egg to help the filling keep its shape in the baked rolls.