In a large pot, bring 4 quarts salted water to a boil. Add cabbage, carrots, and celery and cook until slightly softened, about 2 minutes. Transfer to an ice bath.
Once cool enough to handle, drain and squeeze veggies with a kitchen towel until water is removed; set aside.
In a small bowl, combine soy sauce, hoisin, oyster sauce, and sesame oil.
In a large skillet over medium-high heat, heat vegetable oil until shimmering. Cook garlic and ginger, stirring, until fragrant, about 30 seconds. Add pork and cook, breaking up with a spoon, until browned and starting to crisp, 4 to 5 minutes
Drain fat from skillet until about 1 tablespoon remains. Add soy sauce mixture and toss pork to coat. Cook over medium-high heat, stirring, 1 minute. Add veggies and cook, stirring, until combined and warmed through, 2 to 3 minutes more; season with salt and black pepper. Let cool slightly.
On a clean work surface, arrange an egg roll wrapper in a diamond shape. Spoon 2 heaping tablespoons filling onto bottom third of wrapper. Fold up bottom half and tightly fold in sides. Gently roll and seal edges with a couple drops of water, pressing to adhere.
Working in batches, generously brush egg rolls with vegetable oil. In an air- fryer basket, arrange egg rolls in a single layer. Cook at 400°, flipping halfway through, until golden brown and crispy, about 10 minutes.
Serve egg rolls with mustard and duck sauce alongside.
Notes
These egg rolls can also be oven baked at425ºF for 15 minutes