Pat the chuck roast dry with paper towels and set it aside.
In a small bowl, mix together the chili powder, salt, black pepper, cumin, garlic powder, onion powder, oregano, and cayenne pepper.
Rub the seasoning mix all over the chuck roast, ensuring it's well coated. Set aside.
Heat 2 tablespoons of olive oil in a large skillet over medium heat.
Add the seasoned chuck roast to the skillet and sear it on all sides until browned, about 3-4 minutes per side.
Transfer the browned roast to the insert of your slow cooker.
In the slow cooker, add the diced bell peppers, onions, minced garlic, chipotle peppers, adobo sauce, diced tomatoes with chilies, beef broth, and lime juice.
Cover the slow cooker and cook on LOW for 6 to 8 hours, or until the meat is very tender and falls apart easily.
Once cooked, remove the meat from the slow cooker and place it on a cutting board. Shred the beef using two forks and set aside.
Using an immersion blender, blend the cooking liquid in the slow cooker until smooth and thickened.
Toss the shredded meat with the blended cooking liquid. Taste and adjust seasoning with salt and pepper as needed.
Serve the beef in corn or flour tortillas, topped with cheese, diced onions, lettuce, and sour cream if desired.
Notes
For a milder flavor, reduce the amount of cayenne pepper. Feel free to add your favorite toppings to customize your tacos!