Marinate the cut up chicken in the marinade ingredients for 15-30 minutes.
Combine all the spice mix ingredients in a big bowl.
Mix the coating ingredients well in another large bowl.
When you are ready to cook this dish, cook the broccoli most of the way first and set aside. Heat a work or large skillet over very high heat with a little oil. When smoking, add the broccoli and a pinch of salt and allow to char on one side a little before stir frying. Only cook it briefly so it is still crisp.
Remove the chicken from the marinade and place into the coating and mix well. There shouldn't really be any dry ingredients left after mixing. If there is still liquid, add a little more cornstarch.
Heat your wok over medium high heat and add the oil. Spread the chicken out in the pan so the pieces aren't overlapping. With a spatula or tongs, separate the pieces so they all have space. Leave the chicken without moving until it turns nicely golden on that side.
Flip and cook the other side until brown as well, and then stir fry until cooked through. Move to a plate and reduce heat to medium low.
If there is no more oil in the pan, add a little more. Add the Sichuan peppercorns and stir fry them until dark brown, then skim them out of the pan.
Add the garlic, ginger and scallions and stir fry for 30 seconds. Add in the pepper and spice mix and stir fry briefly. Don't allow the peppers to burn.
Return the chicken and broccoli (if using) to the pan and stir fry for a minute or two to rewarm them. Turn off the heat and add the cilantro. Serve over rice.