Chop bell peppers, carrots, and the white part of the green onions into bite-sized pieces. Mince the garlic. Slice the chicken into thin strips across the grain.

Cook the noodles according to package directions until just al dente. Drain well and toss with a little sesame oil to prevent sticking. Set aside.

Heat a large skillet or wok over medium-high heat. Add 1 tablespoon of sesame oil.

Add the chicken in a single layer and sear for 3 to 4 minutes, then stir and cook for another 2 to 4 minutes until golden and cooked through. Remove the chicken to a plate.

In the same pan, add the bell peppers, carrots, and white parts of the green onions. Stir-fry for 3 to 4 minutes until bright and crisp-tender.

Return the cooked chicken to the skillet. Add the drained noodles, soy sauce, remaining sesame oil if using, minced garlic, and optional sweetener. Toss thoroughly to coat.

Cook for another 1 to 2 minutes, stirring constantly, until everything is heated through. Adjust seasoning with additional soy sauce or rice vinegar. Add red pepper flakes or chili-garlic sauce if desired.

Serve immediately, garnished with green onion tops and a sprinkle of sesame seeds.