Heat a large skillet over medium-high heat. Add oil and swirl to coat. Sprinkle pork with 1/4 teaspoon salt and 1/4 teaspoon pepper. Add pork to pan and cook 10 minutes, turning to brown all sides. Transfer pork to your slow cooker.
Add onion, bell pepper, and garlic, remaining 1/4 teaspoon salt, 1/4 teaspoon pepper, tomatoes, rosemary, and thyme to the slow cooker. Cover and cook on LOW for 7 1/2 hours.
Add vinegar and Worcestershire sauce. Cook, uncovered, for 30 minutes and turn off heat. Shred pork. Serve over polenta or mashed potatoes.