Begin by slicing the boneless, skinless chicken breasts into bite-sized pieces. Toss the chicken with cornstarch, salt, and freshly ground black pepper until well-coated.

Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat. Add the coated chicken pieces in a single layer and sear for 4-5 minutes until browned and cooked through.

In the same skillet, add the remaining tablespoon of oil and heat over medium-high. Toss in sliced onion and bell pepper, stir-frying for 2-3 minutes until tender. Add sliced mushrooms and minced garlic; sauté for another 2-3 minutes.

Whisk together soy sauce, oyster sauce, honey, rice vinegar, and additional black pepper in a small bowl. Pour into the skillet with vegetables, stirring well and cook for 1-2 minutes.

Return the cooked chicken to the skillet and toss everything together for 1-2 minutes on high heat until heated through.

Sprinkle chopped green onions over the stir-fry before serving. Serve hot over steamed jasmine rice or alongside rice noodles.