Prep the chicken: In a small bowl, combine the cornstarch, soy sauce, sesame oil, and black pepper. Add the chicken and toss to coat.

Steam the broccoli: Steam the broccoli until tender-crisp, about 2-3 minutes.

Sauté the chicken: Heat the vegetable oil in a large skillet over high heat. Add the chicken and cook until browned and cooked through, about 3-4 minutes.

Add vegetables and aromatics: Add the garlic and onion to the skillet and cook until fragrant, about 30 seconds. Stir in the steamed broccoli.

Make the sauce: In a small bowl, whisk together the chicken broth and oyster sauce. Pour the sauce over the chicken and broccoli and bring to a simmer.

Serve: Cook for 1-2 minutes, or until the sauce has thickened. Serve immediately.

Optional additions: For a spicier dish, add a pinch of red pepper flakes. For a richer flavor, add a tablespoon of peanut butter or a handful of chopped peanuts.