Heat oil in a large skillet over medium-high heat.
Season chicken with salt and pepper all over and then add to skillet and cook until lightly browned, about 10 to 15 minutes.
Place cooked chicken into slow cooker.
Add remaining ingredients, except cornstarch and water (don't include the noodles/rice); stir to combine.
Cover and cook on HIGH for 3 to 4 hours, or on LOW for 6 to 10 hours.
About 10 minutes before serving, mix together the cornstarch with the water in a small bowl or measuring cup. Add to the slow cooker and stir. Stir occasionally until thickened, about 10 minutes.
Meanwhile, cook the noodles according to the package instructions and then mix them into the chicken mixture. Stir until fully mixed.
Keep on warm until ready to serve, or, serve at once. Garnish with extra sliced scallions, red pepper flakes, and toasted sesame seeds.
