Preheat oven to 220°C (425°F), or 200°C fan.
In a large bowl, whisk cornflour with water until smooth.
Add garlic, ginger, soy sauces, honey, vinegar, black pepper, sesame oil, and olive oil. Mix well.
Add chicken and coat thoroughly in the marinade.
Arrange onion wedges on a baking tray and place chicken on top. Pour remaining sauce over.
Bake for 20 minutes.
Add broccolini to the tray, toss lightly in sauce, and bake for another 8 minutes.
Grill for 2 minutes to caramelize.
Finish with sesame seeds, chilli, and coriander.
This Honey Soy Chicken Tray Bake is best served hot over rice.