Add the chicken and spread it into an even layer.
Cover the skillet, increase the heat to medium-high, and cook, without stirring, for 1 minute.
Stir the chicken and spread it into an even layer. Cover and cook, without stirring, for another minute.
Add the celery and cook uncovered, stirring frequently, until chicken is cooked through, 2 to 3 minutes.
Add the soy sauce mixture and cook, stirring constantly, until the sauce is thickened and shiny and coats the chicken, about 2 minutes.
Stir in the scallions and peanuts. Transfer to a platter and serve.