Heat a large skillet over medium-high heat. Add the ground beef and cook, breaking it up with a wooden spoon, until no longer pink, about 6-8 minutes. Drain excess fat carefully, but leave a little behind for flavor.

In the same skillet, add the diced onion and a splash of water to deglaze any browned bits from the bottom. Cook for 3-4 minutes until softened. Stir in the minced garlic and cook for another 30 seconds until fragrant.

Transfer the beef, onion, and garlic mixture into the slow cooker. Add the cumin, chili powder, smoked paprika, oregano, and black pepper. Stir well to coat everything evenly.

Pour in the beef broth, crushed tomatoes with their juices, and the minced chipotle pepper in adobo. Stir everything together once more to ensure the spices are fully distributed.

Cover and cook on low for 7 hours, or until the beef is tender and the sauce has thickened slightly. The sauce will continue to thicken as it sits after cooking.

Ladle the beef mixture into warm corn tortillas. Top with your favorite extras: diced avocado, a squeeze of lime, fresh cilantro, and a dollop of sour cream or Greek yogurt.