Marinate the chicken: In a medium bowl, blend the soy sauce, dry sherry, and cornstarch until the cornstarch is fully dissolved. Add the chicken pieces and coat them evenly with the mixture. Let it rest at room temperature for 15 minutes, stirring occasionally.

Prepare the sauce: In a separate medium bowl, combine all the sauce ingredients and whisk until the cornstarch is completely dissolved. Make sure to scrape the bottom of the bowl to incorporate any settled cornstarch.

Heat a large nonstick skillet over high heat until it is extremely hot. Pour in 1 tablespoon of the oil and swirl to coat the pan. Add the diced bell pepper, sliced celery, and salt, and stir-fry until the vegetables start to soften and brown slightly, about 5 minutes. Transfer the vegetables to a large bowl and set aside.

Add another ½ tablespoon of oil to the skillet and maintain high heat. Place half of the marinated chicken in the pan, ensuring not to overcrowd it, and cook until one side is browned, about 1½ minutes. Flip the chicken pieces and continue cooking for another 1½ minutes or until fully cooked through. Move the chicken to the bowl with the vegetables. Repeat the process with another ½ tablespoon of oil and the remaining chicken. Once browned and cooked through, add this chicken to the same bowl.

Into the skillet, pour the remaining ½ tablespoon of oil, followed by the chopped garlic and sliced scallions. Stir these with the chicken for about 30 seconds, ensuring they do not burn.

Reintroduce the cooked vegetables and chicken to the skillet, along with the prepared sauce. Lower the heat and simmer until everything is heated through and the sauce has thickened, approximately 30 seconds. Stir in the roasted nuts. Taste the dish and adjust seasoning if needed. If the sauce becomes too thick, thin it with a few tablespoons of water. Serve immediately.