Lamb shoulder and leg are the best cut for making bbq skewers because you can get some large chunks of meat out of them. Cut the lamb into 1-inch size pieces. Don’t cut it too small or else it will dry out quickly while grilling.
Marinade the lamb meat with 2 cups of onion slices and 4 cloves of crushed garlic. Cover it and let it sit for 40 minutes. This is to help gentle some off that strong lamb smell. Also, the enzyme in the onion can tenderize the meat. I have seen people use onion puree instead of the slices. That way the meat will be a bit too wet. When you put wet meat onto a hot grill, it will stick on the grill.
While waiting, you can make the spice powder. Toast 1.5 tbsp of cumin seeds, 2 tsp of Sichuan peppercorn, a tsp of fennel seeds, a tsp of white peppercorn in a cast-iron skillet for 3-5 minutes. Then blend into a fine powder. I always prefer a freshly ground spice mix. It makes a huge difference in taste.
To spice up my BBQ, I also like to use some red chili flake. To get the spicy level that I like, I will mix some mild chili flake with some face heaven chili powder.
Besides that, you will need some salt which we will sprinkle it on while you are grilling.
Put the lamb onto the skewers. Set your grill at high temperature. The thermometer attachment on my grill shows it reaches 500 F. If the temperature is too low, it will take much longer to chared the meat and there is a higher chance that the lamb will be dried out.
Sprinkle some salt. Be generous because some of the salt might fall off while cooking and turning. I will say for 2 pounds of meat, you will need about 2-3 tsp of salt.
It will take a few minutes on each side for it to charred. Once both sides have that nice color, the meat is about medium-rare. The way I like is medium-well so I lower the distance of the charcoal. Let the meat cook for a few minutes more. Keep turning until it reaches the desired color or the doneness that you like.
Once you think it is almost done, you can sprinkle the spice mix and chili flake onto the meat. Take the meat off the grill and enjoy!