Begin by cutting boneless chicken thighs into bite-sized pieces and marinate with freshly ground black pepper and salt for 15 minutes.

In a large skillet, heat a tablespoon of vegetable oil and sear the chicken for 5-7 minutes until golden brown.

In the same skillet, sauté sliced onion and green bell pepper for 2-3 minutes until softened.

Add minced garlic and cook for about 1 minute until fragrant.

Return chicken to skillet, adding soy sauce, oyster sauce, and sugar, cooking for another 2 minutes.

Mix cornstarch with water to create a slurry, then add it to the skillet, stirring until sauce thickens.

Taste the dish and adjust seasoning with salt, then simmer for another 5 minutes.

Transfer to a serving plate, garnish with green onions, and serve hot over rice or noodles.