In a medium-size bowl, mix in egg, soy sauce, shaoxing wine, five spices, brown sugar, and sesame oil. Whisk until well-combined.
Add in the chicken pieces into the mixture, give it a good massage until it's all well-coated. Set aside and let it rest for at least 30 minutes. The longer you marinate it, the better it tastes.
Coating
Heat up the oil for deep frying.
In the meantime, in a ziplock bag, add in the flour, corn starch, baking soda, salt and pepper. Mixed everything until well-combined. I used ziplock bag to coat my chicken so it saves me some dishes :D
Add in the marinated chicken pieces into the flour mixture, zip the ziplock bag and shake the chicken and the flour, and gently massage as you go until all the chicken pieces well-coated.
Deep fry into the pre-heated oil until light golden brown. Transfer the fried chicken on the paper towel to drain the excess oil. For longer crispiness, you can double fry your chicken or toss them in the over for a couple of minutes like I did. Trust me, it stays crispy longer even after coating them with the glaze.
Prepare your steamer and place the bao buns in it, leaving a little space between them so they don’t stick together. Cover and steam for about 8–10 minutes until the buns are soft and heated through. Let the buns stay in the steamer until you are ready to assemble them.
Glazing
In a medium skillet, add in hoisin sauce, soy sauce, honey/sugar, rice vinegar, and water. Stir until well-combined and let it simmer for about 1-2 minutes. Let it cool before coating the crispy chicken.
Once the glaze slightly cools, add in the crispy chicken in the glaze and coat it evenly. Do not soak the crispy chicken.
Assembling
Take the hot buns, and fill in with cucumber slices, julienne green onion, and the glazed crispy chicken. Serve while they are still warm. Enjoy! :)