In a large skillet, heat the olive oil over medium-high heat. Add the beef chunks and sear on all sides until browned, about 5-7 minutes. Transfer the beef to the slow cooker.

In the same skillet, add the chopped onion and garlic. Sauté until the onion is translucent, about 3-4 minutes. Transfer to the slow cooker with the beef.

In a blender, combine the beef broth, diced tomatoes, guajillo chiles, ancho chiles, cumin, oregano, smoked paprika, salt, and black pepper. Blend until smooth.

Pour the blended sauce over the beef in the slow cooker. Add the bay leaves and stir to combine.

Cover and cook on low for 8 hours or on high for 4 hours, until the beef is tender and easily shredded.

Once cooked, remove the beef from the slow cooker and shred it using two forks. Discard the bay leaves. Return the shredded beef to the sauce and stir to combine.

To assemble the tacos, heat the corn tortillas in a dry skillet over medium heat until warm. Fill each tortilla with the shredded beef mixture, and top with chopped cilantro and sliced radishes.

Serve with lime wedges on the side for squeezing over the tacos.