In a small bowl, mix chili powder, paprika, cumin, onion powder, garlic powder, oregano, and salt to make a spice rub.

Place the chuck roast in the slow cooker and rub the spice mix all over the meat.

Add the sliced onions around the roast, then pour in the orange juice and beef broth.

Cover and cook on low for 7–8 hours, or until the meat is tender and easily shreds.

Remove the roast from the slow cooker, shred with two forks, and return the meat to the pot.

Add salsa verde and stir to combine. Serve warm in tortillas with desired toppings.