Preheat oven to 200°C (400°F).
In a bowl, whisk together cornflour and water until smooth.
Add garlic, ginger, light soy sauce, dark soy sauce, honey, vinegar, black pepper, sesame oil, and olive oil. Mix well.
Place chicken thighs, red onions, and broccolini on a large baking tray.
Pour the sauce evenly over everything and toss gently to coat.
Bake for 30–35 minutes, turning once, until chicken is cooked through and caramelized.
Garnish with sesame seeds, chili, and coriander before serving.