Cut tomatillos, onion, and jalapeno into 1-inch pieces. Add vegetables, garlic, cilantro, Worcestershire sauce, salt and pepper to blender. Blend until no large chunks remain. Pour vegetable sauce over pork in slow cooker.
Cover and cook on low for 7 to 8 hours, or on high for 4 to 5 hours.
Remove pork from slow cooker with tongs or slotted spoon to large plate. Shred with two forks. Return to sauce in slow cooker.
Serve immediately on corn tortillas with desired toppings and tomatillo sauce from slow cooker.
Nutrition information does not include tortillas or toppings.
If you prefer, prepare the pork in your oven, using a heavy covered pot, like a Dutch oven. Bake at 300°F for 2 ½ to 3 hours.
For more servings, double all ingredients.
Substitute 2 pounds (or more) of boneless skinless chicken thighs for the pork, if desired.
Alternate serving suggestion: This rich braised pork is delicious served on cilantro lime rice or quinoa. Sprinkle with queso fresco and fresh cilantro.
Stir in a can of white beans, such as Great Northern or cannellini, rinsed and drained, for a more stew-like dish.