1. Evenly season chicken with black pepper and salt. Heat 1 tablespoon canola oil in a large nonstick skillet or wok over medium heat. Add the chicken; cook, stirring occasionally, until lightly browned and a thermometer inserted in the thickest parts 165°F, 7 to 8 minutes. Transfer to a plate. Do not wipe the pan clean.
2. Return the pan to medium heat. Add broccoli and the remaining 1 tablespoon canola oil; stir until the florets are fully coated. Add 1/4 cup water; cover, and cook, undisturbed, until the broccoli is bright green and tender-crisp, about 2 minutes.
3. Whisk broth, hoisin, soy sauce, sesame oil, ginger, garlic, vinegar and white pepper together in a small bowl until fully combined. Pour the mixture over the broccoli; continue cooking over medium heat, stirring occasionally, until the mixture reduces by one-quarter, about 3 minutes.
4. Whisk cornstarch and the remaining 1 tablespoon water together in a small bowl. Add to the pan; cook, stirring constantly, until the sauce has slightly thickened and coats the back of a spoon, about 1 minute.
5. Reduce heat to low. Add the chicken; cook, stirring, until evenly coated and heated through, about 3 minutes. Sprinkle with scallions and sesame seeds.