Start by toasting the dried chilies in a dry skillet over medium heat for about 2-3 minutes until fragrant. Remove stems and seeds, then place them in a blender.
Add the quartered onion, minced garlic, beef broth, cumin, oregano, apple cider vinegar, bay leaves, salt, and pepper to the blender with the chilies. Blend until smooth to create a spicy adobo sauce.
In a large skillet, heat the vegetable oil over medium-high heat. Brown the beef chunks on all sides, about 4-5 minutes each.
Transfer the browned beef to the crockpot and pour the adobo sauce over the beef pieces.
Cover the crockpot and cook on low for 8 hours or on high for 4 hours, until the beef is tender and shreddable.
Once done, remove the bay leaves and shred the beef with two forks. Stir the shredded beef well into the sauce. Adjust seasoning with salt and pepper, if needed.