Pat the chicken dry. Toss with 1 tablespoon oil, 1 teaspoon black pepper, and cornstarch until evenly coated. This creates that delicate crust you'll brag about later.
In a small bowl, whisk soy sauce, oyster sauce, rice vinegar, sugar, chicken broth, and sesame oil. Taste—aim for savory-slightly sweet with a gentle tang.
Use a large wok or skillet over medium-high to high heat. Add the remaining 1 tablespoon oil and swirl until shimmering. We want hot-hot, not timid.
Add chicken in a single layer. Don't overcrowd. Sear 3–4 minutes per side until lightly browned and just cooked through. Remove to a plate.
In the same pan, add onion and bell peppers. Stir-fry 2–3 minutes until crisp-tender. Add garlic, ginger, and chiles (if using). Cook 30 seconds until fragrant.
Put the chicken back in. Sprinkle another 1/2–1 teaspoon freshly cracked black pepper. Stir like you mean it.
Pour in the sauce. Toss until everything is glossy and the sauce slightly thickens, about 1–2 minutes. If it gets too thick, splash in a bit more broth.
Stir in green onions. Taste and adjust pepper, salt, or sugar as needed. It should be pepper-forward, not a salt lick.
Pile over hot jasmine rice or noodles. Garnish with extra green onions and sesame seeds. Proceed to impress yourself.