Making Black Pepper Chicken with Mushrooms is straightforward when you follow these easy steps:

1. Prepare the Chicken: Cut the chicken breasts into bite-sized pieces and set aside.
2. Marinate: In a bowl, mix the chicken, soy sauce, oyster sauce, and half the black pepper. Let it marinate for 10 minutes.
3. Sauté the Garlic and Ginger: Heat 2 tablespoons of vegetable oil in a large skillet over medium heat. Add the minced garlic and ginger, cooking for about 30 seconds until fragrant.
4. Cook the Chicken: Add the marinated chicken to the skillet. Stir-fry for about 5-7 minutes or until the chicken is cooked through and no longer pink in the center.
5. Add the Mushrooms: Toss in the sliced mushrooms and cook for an additional 3-4 minutes, allowing them to soften and release their moisture.
6. Thicken the Sauce: Stir in the cornstarch mixture, and cook for another 2 minutes until the sauce thickens.
7. Add Black Pepper: Season with the remaining black pepper, adjusting to taste. Mix well to ensure everything is evenly coated.
8. Serve: Remove from heat and garnish with chopped spring onions before serving.

These steps will guide you to create a dish that is not only delicious but also visually appealing.