Cook Roast
Arrange onions in crockpot.
Mix garlic powder, chipotle powder, oregano, cumin, and salt.
Rub roast with spice mix.
Place roast over onions.
Pour enchilada sauce over roast.
Add chipotle peppers and butter.
Cook on LOW for 5 hours or HIGH for 3 hours.
Remove meat and shred.
Make Sauce
Combine all sauce ingredients in a blender.
Pulse until combined, do not puree.
Season with salt.
Assemble Tacos
Stuff taco shells with shredded beef and onions.
Top with sauce, cilantro, avocado, and cheese.
Serve with braising liquid.
