Begin by slicing the boneless chicken thighs into bite-sized pieces. In a mixing bowl, combine the chicken with freshly ground black pepper and a sprinkle of salt. Let the chicken marinate for at least 15 minutes.

In a large skillet or wok, heat 2 tablespoons of vegetable oil over medium-high heat. Add the marinated chicken and sauté until it turns golden brown, approximately 5-7 minutes.

Once the chicken is browned, remove it from the skillet. Add the sliced onion and green bell pepper and stir-fry for 2-3 minutes until they soften.

Push the vegetables to one side of the skillet and add the minced garlic to the center. Stir for about 1 minute.

Return the partially cooked chicken to the skillet, mixing it with the sautéed vegetables. Pour in the soy sauce, oyster sauce, and sugar, stirring well.

Create a cornstarch slurry by mixing cornstarch with water in a small bowl. Pour this into the skillet and stir until the sauce thickens, about 1-2 minutes.

Taste your Black Pepper Chicken and adjust seasoning, adding salt if needed. Continue cooking for another 5 minutes.

Remove from heat and transfer to a serving dish. Garnish with freshly chopped green onions. Serve hot with rice or noodles.