Toast all the spices (Dried Chilies, Sichuan peppercorn, coriander seeds, cinnamon stick, orange peel) in a wok over medium-low heat for a couple of minutes. Remove them from the wok and let it cool.
Add 2 tsp of roasted cumin seeds then blend all the spices into a fine powder. If your cumin is raw, toast it in the wok with other spices.
Take 1 tsp of the spice powder and mix with 1/2 tsp of roasted cumin seeds, and 1/2 tsp of roasted sesame seeds. Reserve this to sprinkle onto the lamb at the end.
Add 2 tsp of salt, 1/2 tsp of sugar, and 1 tsp of garlic powder to the rest of the spicy powder. Mix thoroughly. Then sprinkle this dry rub all over the lamb ribs and pad it down. You can also use lamb leg, I once tried this season on a piece of beef chuck roast. It tastes amazing too.
Wrap the lamb ribs with a couple of layers of tin foil. You can marinade it overnight but it is not necessary. You can bake it right away.
Preheat the oven to 250 F. Put the lamb in the middle rack of the oven. Meat side down. Bake for 2 hours.
2 hours later, take the lamb out and unwrap the tin foil. Pour the juice from the tin foil into a baking tray, add the onion or other vegetables that you like. Put the lamb rack on top of the onion with the meat side up.
Put it back into the oven. Bake it at 420 F for 20 minutes. This will help to brown the outside, render the fat from the fat cap, and create a crispy layer.
Sprinkle the reserved dry rub on the top of the lamb and put the cilantro around it. Let it rest for at least 20 minutes before you cut it to serve.