In a dry pan, toast the cumin seeds, sichuan peppercorns, and red chili flakes. Crush into a coarse powder with a mortar & pestle or spice grinder. Set aside.
Combine about half of your spice mixture with the lamb, and form into 4 patties. Season both sides of each patty with salt.
Heat a grill or cast iron skillet over high heat until searing hot. Sear the burgers until crisp on both sides, about 1-2 minutes per side.
Set aside on a plate to rest, and cover with foil. Add the onion and peppers to the pan along with a little vegetable oil (if you used a cast iron skillet), and fry until caramelized. If you grilled your burgers outdoors, just fry the onions and peppers in a separate pan. Sprinkle with half of the remaining spice mixture.
Combine the yogurt with the garlic and season with salt to taste. Stir in the rest of the spice mixture.
To assemble the burgers, spread some of your yogurt mixture on the bottom of the bun, and top with some diced cucumbers. Top with the burger, the onion/pepper mixture, more yogurt, and fresh cilantro. Serve!