1. In a bowl, combine the chicken pieces with soy sauce, oyster sauce, and black pepper. Let it marinate for at least 20 minutes, allowing the flavors to meld.
2. Heat a tablespoon of vegetable oil in a large skillet over medium-high heat. Add the marinated chicken and cook until browned and cooked through, about 5-7 minutes. Remove the chicken from the skillet and set aside.
3. In the same skillet, add another tablespoon of oil. Sauté the onions and garlic until fragrant and translucent, about 2-3 minutes.
4. Add the mushrooms and bell pepper to the skillet, cooking until the mushrooms are golden and the bell peppers are tender, about 5 minutes.
5. Return the chicken to the skillet. Stir in the cornstarch mixture and chicken broth, bringing the sauce to a simmer. Cook until the sauce thickens, coating the chicken and vegetables beautifully.
6. Season with additional salt if needed, and adjust the pepper for a spicier kick.

Remember, cooking is about using your senses, just like my abuela taught me. Listen for the sizzle, smell the spices, and taste as you go.