In a very large (12-inch) skillet, heat the avocado oil over medium-high heat. Pat the lamb dry with a paper towel and sprinkle generously with salt and pepper. Sear lamb on all sides. Make sure that each side of the lamb is deeply browned before you turn it. This is very important for flavor. This step will take you about 10 minutes.
As soon as lamb is nicely browned, place it in the crockpot on top of a layer of sliced onion. Deglaze hot skillet with broth or beer, getting up all the brown bits.
Combine all the marinade ingredients in a blender with 1 cup of water and blend to a smooth puree. Layer the top of the lamb with marinade allowing it to drizzle over the sides as well. Pour the beer or stock mixture from skillet around the lamb to coat the bottom of the crockpot (don’t drizzle the mixture on top of the lamb because we want the marinade to stay intact and flavor the meat as it cooks.)
Cover and turn the crockpot to low. Your barbacoa will be done in about 8 hours.
When you are ready to serve, coarsely shred the lamb and arrange it on a warm platter. Drizzle some of the liquid in the bottom of the crockpot over the lamb and don’t forget to scoop up those delicious onions on the bottom.
Check and make sure you don’t need any additional salt. Serve the barbacoa with salsa, guacamole, and some feta cheese. Onion and cilantro are a great addition as well. Grab some tortillas, if you like, and you’re ready to make some delicious tacos.