Fill a large pot with lightly salted water and bring to a rolling boil.
Stir in whole-wheat noodles and return to a boil. Cook uncovered, stirring occasionally, until the pasta has cooked through but is firm to the bite, 5 to 8 minutes. Drain well and set aside.
Combine chicken stock, orange marmalade, tamari sauce, whole ginger root piece, and ground black pepper in a pot over medium-high heat.
Bring sauce to a boil and reduce heat to medium. Simmer until sauce reduces and thickens; about 20 minutes.
Remove sauce from heat. Stir in lemon juice and set aside.
Heat peanut oil in a large skillet over medium-high heat.
Cook and stir chicken in hot oil until golden, no longer pink in the center, and the juices run clear, 5 to 10 minutes.
Remove chicken from skillet and set aside, leaving oil in the pan.
Cook and stir the stir-fry vegetables in the same skillet used for the chicken until vegetables are almost tender, 4 to 5 minutes.
Remove ginger root piece from sauce and discard.
Stir chicken and sauce into vegetables and cook until heated through, 1 to 2 minutes.
