Heat a frying pan, dry over a moderate heat until hot.
Place the cumin, chilli flakes, black peppercorns and Sichuan peppercorns and toast dry for 1-2 minutes. Remove from the pan and add to a spice/coffee grinder or pestle and mortar.
Grind the spices into a rough texture (see pic above).
Stir in the chilli powder, ginger powder, garlic and salt.
Pour over the oil and mix to combine well. Set aside.
How to make the skewers
Add the spice rub to the lamb cubes and massage into the meat with your hands to coat all the lamb well. Place in a bag and refrigerate for as long as you can - 4 hrs minimum, 24 hours is BEST!
If you're using wooden skewers, now is the time to soak these in water, to ensure they don't disintegrate on the grill.
Once marinated, thread cubes of meat (and fat) onto the skewers (about 8-10 pieces per skewer).
Cook on a hot BBQ grill or hot oven grill for about 10-12 minutes, turning regularly.
Remove from the grill, rest for a couple of minutes and serve!