Heat the oil in a large skillet over medium-high heat. Add the chuck roast and season with salt, pepper, garlic powder, and ground cumin. Sear both sides of the beef until it is nicely browned (about 2 minutes per side).
Add 1 tablespoon of oil to another large skillet. Once hot, add the quartered onion, garlic cloves, serrano peppers (or jalapenos), and Roma tomatoes. Sauté for about 5 minutes until the vegetables are softened.
Transfer the sautéed vegetables to a blender along with 2 cups of water and blend until smooth. Add the blended mixture back to the skillet and reduce heat to medium-low. Simmer for 15 minutes and season with salt and pepper to taste.
Transfer the seared beef to a large pot and add 4 cups of water, bay leaves, Worcestershire sauce, roasted poblano pepper slices, and sliced onion. Bring to a boil and reduce heat to low. Simmer until the beef is extremely tender (about 2-3 hours).
Once the beef is cooked, shred it using a fork and add it to the tomato sauce. Simmer for an additional 10 minutes and serve with warm tortillas or rice.