Preheat the oven to 350°F.

In a Dutch oven, stir together the chopped chipotle chiles, ketchup, tomato paste, chopped garlic, oregano, chili powder, salt, and black pepper until evenly combined.

Cut the trimmed 3‑pound beef chuck roast into 4 equal pieces and place them in the Dutch oven. Turn each piece to coat it thoroughly with the sauce.

Set the Dutch oven over medium-high heat and bring the sauce to a gentle simmer, 1–2 minutes, to heat through and loosen the sauce.

Cover the Dutch oven with its lid and transfer it to the preheated oven. Bake until the beef is very tender and can be shredded with two forks, about 2 1/2 hours. (Occasionally tilt the pot and spoon sauce over the meat if the top begins to dry.)

Remove the Dutch oven from the oven. Use two forks to shred the beef, mixing the shredded meat with the sauce in the pot.

Serve the shredded beef for tacos and, if desired, sprinkle with chopped fresh cilantro and sliced green onion.