In a mixing bowl, combine the chipotle chiles, ketchup, tomato paste, garlic, oregano, chili powder, salt, and black pepper. Stir until well combined and set aside.
In a hot skillet over medium-high heat, sear the beef chuck roast on all sides until browned, about 4-5 minutes per side.
Place the beef in the slow cooker or Dutch oven. Pour the sauce mixture over the beef, ensuring it’s well-coated.
If using a slow cooker, set it to low and cook for 8 hours or high for 4 hours. If using a Dutch oven, cover and cook in a preheated oven at 300°F (150°C) for about 3-4 hours, or until the beef is fork-tender.
Once cooked, remove the beef from the cooker and let it rest for a few minutes. Shred the beef into bite-sized pieces, mixing it back into the sauce.
Spoon the Chipotle Beef into warm tortillas, and top with your favorite garnishes like chopped cilantro and sliced green onion.
