Prepare the sauce Create the black pepper sauce by blending together crushed black pepper, rice vinegar, soy sauce, brown sugar, toasted sesame oil, cornstarch, and water in a bowl until the mixture is smooth with no lumps.

Marinate the chicken Cover the chicken with a tablespoon of the prepared sauce, two tablespoons of cornstarch, and salt. Allow it to rest while you prepare the onion, ginger, garlic, and pepper.

Brown the chicken Heat a large frying pan over high heat. Add a tablespoon of oil and spread it evenly across the pan. Place the chicken in a single layer and cook over medium heat until golden on one side. Flip the chicken cubes and continue cooking until they are nearly cooked through and browned. Transfer the cooked chicken to a plate, making sure not to overcrowd the pan; cook the chicken in batches if necessary.

Stir-fry the vegetables Using the same pan, heat another tablespoon of oil. Add ginger, garlic, and chopped chilies, and sauté for 30 seconds. Quickly add the onion and bell peppers, stirring frequently over high heat until the vegetables are crisp-tender.

Combine Reduce the heat to low. Whisk the sauce mixture again and pour it into the pan. Let it simmer for 30 seconds. Add the cooked chicken back into the pan and toss everything together until the chicken is heated through.

Serve Turn off the heat and sprinkle freshly ground black pepper over the dish. Stir to combine and serve immediately while hot.