Prepare the spice mix: Add the Chinese chili flakes, cumin powder, fennel seeds, and Sichuan peppercorns into a small bowl. Mix well.

Prepare the lamb patty: In a large bowl, add the ground lamb, the spice mix and salt. Use your hand to mix thoroughly to evenly distribute the spice. Divide the spiced lamb meat into 3 even balls (*Footnote 1). Shape each ball into a burger patty, and place meat in the fridge.

Mix the burger sauce: Combine the kewpie mayo, chili crispy, ketchup and vinegar in a small bowl. Stir to mix well.

Cook the burger buns: Toast the burger buns in a 350°F (176°C) oven until warmed through.

Cook the burger patties: Heat oil in a heavy pan (or a grill), preferably a cast iron pan, over medium-high heat until shimmering. Cook lamb patties in batches. Carefully lay the patties in the pan, press down on them to sear the bottom until browned, 2 minutes or so. Flip the burgers, press and cook for 1 minute. Add the cheese slice and cook for another minute, until the bottom has browned and the cheese melted. Cook the rest of the patties the same way.

To assemble: Spread a generous amount of burger sauce on both cut sides of the burger buns. On the bottom bun, add lettuce, onion, tomato, and burger patty with cheese, finishing with the top bun. Enjoy!