Heat the vegetable oil in a large skillet or wok over medium-high heat.
Add the sliced chicken to the skillet and season with salt and pepper. Cook for about 5-7 minutes, or until the chicken is browned and cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add the green beans and red bell pepper. Stir-fry for about 3-4 minutes until the vegetables are tender-crisp.
Add the minced garlic and ginger to the skillet, stirring for about 30 seconds until fragrant.
Return the cooked chicken to the skillet. Pour in the soy sauce, oyster sauce, and sesame oil, stirring to combine.
Add the cornstarch mixture to the skillet and cook for an additional 1-2 minutes until the sauce thickens.
Serve the stir-fry over cooked rice or noodles.