1-Step 1: Prepare and Season the Chicken Start by placing 2 lbs of boneless skinless chicken thighs in a large bowl. Cut the chicken into uniform 1-inch cubes if you haven’t already. Uniformity matters here because it ensures even cooking throughout the dish. Add the cornstarch, 1 tablespoon of soy sauce, kosher salt, and ground black pepper to the bowl. Toss everything together until each piece of chicken is evenly coated with the mixture. The cornstarch might seem like a small detail, but it’s what gives the chicken that beautiful golden exterior while keeping the inside incredibly juicy. Let the coated chicken sit for about 10 minutes while you prepare the other ingredients. This brief rest allows the cornstarch to form a better bond with the meat, resulting in a superior crust when seared.

2-Step 2: Heat the Pan and Sear the Chicken Heat 2 tablespoons of vegetable oil in a large skillet or wok over medium-high heat. Wait until the oil starts to shimmer before adding any chicken. A properly heated pan is crucial for achieving that golden-brown sear rather than steaming the meat. Working in batches, add the chicken in a single layer. Overcrowding the pan is a common mistake that leads to soggy, unevenly cooked chicken. Each piece needs space around it to brown properly. Sear the chicken until golden brown on all sides, about 3 to 4 minutes per batch. Add more vegetable oil as needed between batches. Transfer the cooked chicken to a clean plate and set it aside while you continue with the remaining pieces.

3-Step 3: Cook the Mushrooms and Aromatics Once all the chicken is seared and removed from the pan, heat the remaining 1 tablespoon of oil over medium-high heat. Add the sliced mushrooms and green onions to the hot pan. Cook them for 2 to 4 minutes until the mushrooms are tender and have released some of their moisture. Mushrooms contain a lot of water, and allowing them to cook properly concentrates their flavor. You’ll notice them shrinking and becoming more fragrant as they cook. The green onions will soften and become slightly caramelized. Add the minced garlic and grated ginger to the pan. Cook these aromatics for just 1 minute until fragrant. Garlic burns quickly and becomes bitter, so keep a close eye on it. Remove the pan from heat briefly if needed to prevent overcooking.

4-Step 4: Prepare and Add the Sauce While the mushrooms cook, whisk together the sauce ingredients in a small bowl. Combine the remaining 1/3 cup soy sauce, light brown sugar, sesame oil, oyster sauce, and rice wine vinegar. Whisk until completely smooth and the sugar has dissolved. This sauce mixture is the flavor powerhouse of your mushroom pepper chicken. Each ingredient plays a specific role: soy sauce provides saltiness, brown sugar adds sweetness, sesame oil contributes nutty depth, oyster sauce brings umami richness, and rice wine vinegar provides brightness. Return the pan with mushrooms to medium-high heat. Add the seared chicken back to the pan along with the sauce mixture. Toss everything together for 2 to 3 minutes. The sauce will bubble and thicken as it coats the chicken and mushrooms. The cornstarch on the chicken helps create a glossy, clingy sauce that doesn’t slide right off.

5-Step 5: Final Seasoning and Serving Taste the finished dish and season with additional coarsely-ground black pepper and kosher salt as needed. Freshly ground pepper makes a significant difference here because it has more intense flavor and aroma than pre-ground pepper. Serve your black pepper chicken stir fry immediately over steamed rice. Top with additional sliced green onions for a fresh finish and a pop of color. The dish is best enjoyed right away while the chicken still has its crispy exterior and the sauce is at its glossiest.