Pat the chicken dry with paper towels. If you have time, a quick dusting with a pinch of salt and a teaspoon of cornstarch helps it stay juicy during cook time.
Heat a large skillet or wok over medium-high heat. Add 1 tablespoon of oil and swirl to coat. Add the chicken in a single layer; don’t crowd the pan. Cook until lightly browned and just cooked through, about 4–6 minutes. Transfer to a plate.
In the same pan, add the remaining oil. Toss in the garlic and ginger, letting them bloom for about 30 seconds until fragrant. If you’re using Szechuan pepper, grind it fresh and add it now for a subtle numbing heat.
Stir in the doubanjiang and cook for another 30 seconds to wake up the chili paste. It’ll smell tangy and spicy.
Return the chicken to the pan. Pour in the rice vinegar, soy sauce, oyster sauce, and sugar. Stir to coat everything evenly.
Mix the cornstarch with the water to create a slurry, then pour it into the pan. Stir until the sauce thickens to a glossy coating, about 1–2 minutes.
Add the bell peppers, carrots, and most of the scallions. Stir-fry for 2–3 minutes until the vegetables are just tender but still bright. Finish with a drizzle of sesame oil.
Taste and adjust with salt or a pinch more soy if you like. Remove from heat and scatter the remaining scallions on top for color.