In a dry skillet over medium heat, toast cumin seeds and peppercorns for about 1 minute or until fragrant. Coarsely grind toasted spices in a spice grinder or with a mortar and pestle. Mix with salt and chili flakes.
Add spice mixture to sliced lamb and toss to coat evenly.
Heat a large skillet or wok over high heat until hot. Add oil and when it just starts to smoke, add onions. Cook and stir about 2 minutes until the edges are translucent. Transfer onions to a bowl.
Add lamb with spices to the wok; cook and stir until meat starts to brown, about 2 minutes. Add green onions, garlic, soy sauce and wine; bring to simmer. Cook and stir 2 minutes more or until lamb is just cooked through. Add onions and stir to combine. Remove from heat and stir in cilantro. Transfer to platter and serve.