Set up the steamer: Fill a steamer pot with 1½ cups (355 ml) water, or just enough water to sit below the steamer rack without touching the plate. Place the steamer rack inside, cover, and bring the water to a boil over medium-high heat.
Arrange the chicken: While the water heats, place a small heatproof cup upside down in the center of a large heatproof dish. Use a low-walled dish that is deep enough to hold the chicken juices; avoid a flat plate. Arrange the chicken around the cup. Scatter the ginger, garlic, and scallion whites over and around the chicken. Drizzle with rice wine.
Steam the chicken: Once the water is boiling, reduce the heat to medium. Carefully place the dish with the chicken onto the steamer rack. Cover and steam for 30 minutes total. Start on medium heat. Once you see steady steam escaping, about 5 minutes in, lower the heat to medium-low or low and continue steaming gently.
Prepare the cucumber: While the chicken steams, julienne the cucumbers. Transfer them to a bowl of ice water and chill in the fridge to keep them crisp.
Prepare the aromatics: Dice the scallion, finely mince the garlic, and slice the chili pepper, if using. Transfer them to a small heatproof bowl with the sesame seeds.
Heat the oil: In a small, heavy-bottomed saucepan, add the neutral oil. Warm it over medium-low heat for 7 to 8 minutes, or until the oil shimmers. To test, insert a dry chopstick into the oil. If small bubbles form around it, the oil is ready.
Sizzle the aromatics: Slowly and carefully pour the hot oil over the aromatics. The mixture will sizzle right away. Stir with a spoon to combine, then set aside.
Check the chicken: Insert a digital thermometer into the thickest part of the chicken, avoiding the bone. The chicken should register at least 165°F (74°C).
Cool the chicken: Turn off the heat. Do not move the center cup yet. Carefully transfer the chicken to a large bowl of room-temperature water and let it sit until cool enough to handle. Discard the steamed ginger, garlic, and scallion from the plate.
Save the chicken juice: Once the chicken and steamed aromatics are removed from the plate, carefully lift out the center cup. The clear, concentrated chicken juices will gather in the center of the dish. Save this chicken juice to loosen and flavor the sauce.
Make the sauce: To the bowl with the sizzling aromatics, add the salt, sugar, soy sauce, sesame paste, and black vinegar. Stir well. Add 1½ tablespoons of the reserved chicken juice first, then add more as needed until the sauce is loose, pourable, and lightly thickened. It should not look creamy or heavy at this stage. Keep it on the thinner side because the sesame paste will continue to thicken, and the shredded chicken will absorb some of the sauce after tossing.
Shred the chicken: Drain the cooled chicken and shred the meat into strips. Discard the bones and skin.
Plate and serve: Drain the cucumber well and place it on a large serving plate. Add the shredded chicken on top. Pour the sauce over the chicken. Garnish with cilantro, extra sesame seeds, and a small drizzle of toasted sesame oil. Toss before serving. Serve at room temperature or slightly chilled.
Notes
Why steam the chicken instead of boiling it: Steaming keeps the chicken tender and juicy because the flavor stays with the meat instead of leaking into a pot of water. In my recipe testing, steaming gave the chicken a better taste and texture. It also gives us a small amount of concentrated chicken juice to use in the sauce.
Why place a small cup in the center: The small cup helps the chicken juices collect instead of spreading too thinly across the plate. After steaming, save the concentrated juices from the dish. This is the chicken essence that gives the sauce extra depth and body.
About the liquid after steaming: Right after steaming, you may see some liquid gathered on the plate. Don’t pour it away. Give it a few seconds to settle, then save the golden chicken juice for the sauce. This is one of the best parts of the recipe.
Make-ahead: You can steam and shred the chicken in advance. Store the shredded chicken and reserved chicken juice separately in the fridge. For the best flavor and texture, make the sizzling aromatics and sauce the day you plan to serve.
Storage: Once mixed with the cucumber and sauce, store the salad in an airtight container in the fridge. It is best finished within 1 to 2 days while the cucumber is still crisp.
Reheating: This dish is not meant to be reheated because of the fresh cucumber. In Taiwan, bang bang chicken is commonly enjoyed cool or at room temperature, especially during hot weather.