Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat.
Add the chicken pieces and season with salt. Cook until browned and cooked through, about 5-7 minutes. Remove the chicken from the skillet and set aside.
In a small bowl, mix cornstarch, soy sauce, oyster sauce, rice vinegar, and black pepper. Stir until well combined.
In the same skillet, add the remaining tablespoon of oil. Sauté the garlic and ginger for about 30 seconds until fragrant.
Add the bell pepper and cook for another 2-3 minutes until slightly tender.
Return the chicken to the skillet and pour the sauce mixture over it. Stir well to coat the chicken and vegetables.
Cook for an additional 2-3 minutes until the sauce thickens slightly.
Add the green onions and stir to combine. Cook for another minute, then remove from heat.
Serve hot over steamed rice or noodles.