Step 1

Trim fat from roast. With a sharp knife, make slits evenly on all sides of the roast. Insert garlic slices into slits. Place roast in a 3-1/2- or 4-quart slow cooker (see Tip).

Step 2

In a blender combine vinegar, cilantro, onion wedges, the water, oregano, cumin, salt, and pepper. Cover and blend until smooth. Pour over meat in slow cooker.

Step 3

Cover and cook on low-heat setting for 10 to 12 hours or on high-heat setting for 5 to 6 hours.

Step 4

Just before serving, in a large skillet cook red onions in hot oil about 15 minutes or until tender. Carefully add lime juice to skillet. Cook and stir for 3 to 5 minutes or until lime juice is evaporated.

Step 5

Meanwhile, using a slotted spoon, remove meat from slow cooker and place on cutting board. Shred meat by pulling two forks through it in opposite directions; discard any fat. Transfer shredded meat to a large bowl. Add 1 cup of the cooking liquid remaining in slow cooker, tossing to coat.

Step 6

Spoon about 2/3 cup shredded meat onto each roll bottom. If desired, drizzle with additional cooking liquid. Top with cooked red onions and roll tops.