ENCHILADA SAUCE: Heat small pot over medium heat. Remove stems from guajillo, cut to remove seeds.
Toast in heated pot, stir and be careful not to burn or they become bitter.
Preheat broiler. Put onions, tomatillos, tomatoes and garlic for the enchilada sauce and for the lamb filling on a baking sheet. Put baking sheet in broiler; cook without turning vegetables until they start to get charred, about 5-8 minutes. Remove, set aside the vegetables for the lamb filling. Add all the ingredients for the Enchilada Sauce to a blender. Blend until smooth. Add this to the bottom of the slow cooker.
LAMB FILLING: Season lamb with salt and pepper, sear on all sides in the slow cooker or in a pan. If cooking in a pan, transfer lamb to the slow cooker and turn on high. While slow cooker is coming to temperature, put roasted/charred vegetables in blender and puree until smooth. Carefully open slow cooker, as there will most likely be steam. Pour vegetable puree over lamb in the slow cooker and cook for 4–6 hours.
When lamb is fork-tender and falling apart, turn off slow cooker and let cool for 30 minutes. Using tongs and a fork, shred lamb. Turn slow cooker back on to warm setting.
ASSEMBLY: Warm tortillas. To serve, fill tortillas with lamb and top with cilantro, onions, radishes and lime juice.
