In a heavy-bottomed pot, heat the olive oil over medium-high heat. Add the chunks of beef and sear them until they develop a rich brown crust, approximately 5-7 minutes. Once browned, remove the beef and set it aside on a plate.
In the same pot, toss in the diced onion and minced garlic, sautéing until they become fragrant and translucent, about 3-4 minutes.
While the onions are cooking, place the guajillo and ancho peppers in a blender with the beef stock. Blend until the mixture is smooth and well-combined.
Return the seared beef to the pot and pour the blended pepper sauce over it. Sprinkle in the cumin, oregano, smoked paprika, sea salt, black pepper, and cinnamon. Mix everything thoroughly.
Bring the mixture to a gentle simmer, cover the pot, and lower the heat. Allow it to cook for 2-3 hours, or until the beef is fork-tender and can be easily shredded.
Once the beef is ready, shred it using two forks and stir it back into the flavorful broth.
To prepare the tacos, heat a skillet over medium heat. Lightly dip each corn tortilla into the broth, then place it in the skillet. Add a generous portion of the shredded beef and top with fresh cilantro and diced onion. Fold the tortilla and cook until it’s crispy and golden, about 2-3 minutes on each side.
Serve the tacos with lime wedges on the side for an extra zesty kick.