In a large skillet or Dutch oven, heat the vegetable oil over medium-high heat.
Add the chopped onion and minced garlic, sauté until fragrant and translucent.
Add the beef chuck roast and sear it on all sides until it's nicely browned.
Stir in the diced tomatoes, red bell pepper, ground cumin, chili powder, paprika, salt, and pepper.
Reduce the heat to low, cover, and simmer for 3 hours, or until the beef is tender and can easily be pulled apart with a fork.
Once the beef is tender, use two forks to shred it into pulled beef.