Begin by cutting boneless chicken thighs into bite-sized pieces and seasoning them with black pepper and salt. Marinate for at least 15 minutes.

Heat vegetable oil in a skillet over medium-high heat until it shimmers. Add marinated chicken and sauté for 5–7 minutes until golden brown. Set aside.

In the same skillet, add sliced onion and green bell pepper. Stir-fry for 2–3 minutes until they soften.

Add minced garlic and sauté for 1 minute until fragrant. Avoid burning the garlic.

Return the chicken to the skillet, add soy sauce, oyster sauce, and sugar. Cook for another 2–3 minutes until chicken is cooked through.

Mix cornstarch with water to create a slurry. Pour into the skillet while stirring to thicken the sauce.

Adjust seasoning with salt if needed. Simmer for 3–5 minutes until fully cooked.

Garnish with chopped green onions and serve over rice or noodles.