Step 1: Boil a large pot of salted water and cook the spaghetti for one minute less than the package directions until al dente. Drain and set aside.
Step 2: In a small bowl, whisk together the soy sauce, dark soy sauce, oyster sauce, and brown sugar to create the sauce base.
Step 3: Heat 1 tablespoon of vegetable oil in a wok or large skillet over high heat. Add the sliced chicken and stir-fry until golden and cooked through. Remove chicken from the pan and set aside.
Step 4: Add the remaining 1 tablespoon of oil to the same pan. Stir-fry the garlic, ginger, and the white parts of the green onions for 30 seconds.
Step 5: Add the cabbage, carrots, and bell peppers to the wok. Stir-fry for 2-3 minutes until the vegetables are slightly softened but still crisp.
Step 6: Return the cooked chicken and the boiled spaghetti to the wok. Pour the sauce mixture over the ingredients.
Step 7: Toss everything together over high heat for 1-2 minutes until the sauce is well-combined and the noodles are glossy.
Step 8: Remove from heat, stir in the green parts of the scallions and the sesame oil. Serve immediately.