To Make the Dipping Sauce:

1. Whisk together all of the ingredients in a small saucepan. Bring to a boil over medium heat, stirring often. When mixture reaches a boil, cook for another minute. Remove from heat and set aside.

To Make the Filling:

1. Add the sesame oil for the egg rolls to a wok or large frying pan and place over medium-high heat. Once hot, saute the celery, onion, garlic, shredded cabbage, carrots, mushrooms, and green pepper for approximately 5 minutes, until vegetables are softened and onions are translucent.
2. Add the bean sprouts and cooked chicken, then turn off the heat. If making ahead, transfer the mixture to a bowl, cool to room temperature, cover, and refrigerate.

To Assemble:

1. Lay an egg roll wrapper flat on a clean work surface, with a corner pointing towards you, like a diamond. Place 4 tablespoons of filling near the corner closest to you.
2. Moisten each edge of the square with a finger dipped in water. Lift the bottom corner up and begin to roll away from yourself, making sure to tuck the corner under the filling as you roll. 
3. Once you have rolled up the wrapper about halfway, fold in the left side, and then the right side, towards the center. Continue rolling away from you until the final corner is rolled up.
4. Dip your finger in water and brush it over the final corner, pressing the seam to ensure it is sealed.
5. Proceed with the remaining egg roll wrappers and filling. 

To Fry:

1. In a large frying pan over medium-high heat or in a deep fryer, heat oil to 350˚F.
2. Add egg rolls in batches of 3 to 4 at a time, to avoid overcrowding. Fry until golden and crispy, about 3 to 4 minutes. Remove and place on a paper towel-lined plate to drain.
3. Serve immediately, with dipping sauce.