In a small bowl, combine kosher salt, garlic powder, onion powder, paprika, cumin, oregano, and red pepper flakes.
Pat the chuck roast cubes dry with a paper towel and season them on all sides with the dry rub, making sure each piece gets coated evenly.
Add the beef to the slow cooker with the beef stock, sliced onion, garlic, and bay leaves.
Cook on high for 4 hours, or low for 6 hours, or until the beef easily shreds with a fork.
To crisp the beef, drain the beef and remove the garlic and bay leaves and shred the beef.
Heat a large skillet over medium-high heat and add the olive oil.
Once the skillet is hot, add the beef and cook, stirring occasionally, for 5-7 minutes or until the beef is browned and crisp in some areas.
Enjoy immediately, with your choice of toppings.