Thinly slice the chicken breasts or thighs and transfer it to a bowl. Coat the chicken with 1 tbsp light soy sauce, 1/2 tbsp cornstarch and 1 tbsp cooking oil. Set aside to marinate for 15 minutes.
Thinly slice 1 large carrot and bell pepper (any color). Slice the white parts of 4 scallions/green onions lengthwise. Cut the green parts into 2-inch pieces.
Combine all the lo mein sauce ingredients in a bowl and set aside.
Cook 10 oz egg noodles according to the package instructions. Drain and rinse under cold water until cooled. Toss the noodles with some oil to prevent sticking.
Heat 2 tbsp of oil in a wok or large pan over medium-high heat. Add the marinated chicken and stir-fry until fully cooked through. Transfer to a bowl.
In the same wok or pan, add the scallion whites and stir-fry for about 1 minute. Add 2 tbsp minced garlic and cook for another 30 seconds or until fragrant. Add the thinly sliced carrot and stir-fry until it turns a bright orange. Add the sliced bell pepper and stir-fry for about 2 minutes or until slightly tender.
Return the cooked chicken to the wok or pan and mix well. Pour in the lo mein sauce and cook until it slightly thickens.
Add the cooked noodles and toss everything together until the noodles are evenly coated with the sauce.
Add the green tops or the scallions/green onions and mix well. Drizzle in 1/2 tsp of toasted sesame oil and give everything a final toss.