In a bowl or baking dish, toss chicken with 1 cup orange juice concentrate, cornstarch, chili garlic sauce, and ginger. Cover and refrigerate for 1 hour.
Cook the noodles according to package directions. Drain and hold in a bowl of cold water.
Remove chicken from refrigerator and drain into a colander; discard marinade.
In a large skillet, combine chicken stock, remaining 1/4 cup orange juice concentrate, and oyster sauce. Cook sauce over medium-high heat until liquids reduce and sauce is thick, about 5 to 10 minutes.
While sauce is reducing, heat 1 tablespoon oil in a large skillet over high heat. Add red pepper, peas, mushrooms, and green onions. Saute until tender yet still crisp. Remove from the heat and set aside.
Heat a non-stick wok or large skillet over high heat. Add remaining 1 tablespoon oil to the pan and heat. Carefully drop 1/3 of the chicken into the wok and stir-fry so that all sides of the chicken get crispy. When the first 1/3 is fully cooked through, remove from pan and repeat with the remaining 2 portions.
Add all of the cooked chicken and sauteed vegetables to the skillet with the sauce and toss to combine.
Drain noodles and then add to pan with sauce. Stir to coat noodles with sauce. Transfer to a large serving platter.
