Top-ranked recipe named "Charley's Slow Cooker Mexican Style Meat (Crockpot)"
Trim the roast of any excess fat, and season with salt and pepper. Heat olive oil in a large skillet over medium-high heat. Place meat in hot skillet, and brown meat quickly on all sides.
Transfer the roast to a slow cooker, and sprinkle onion over meat. Season with chile peppers, chili powder, cayenne pepper, hot pepper sauce, and garlic powder. Add enough water to cover 1/3 of the roast.
Cover, and cook on High for 6 hours, checking to make sure there is always at least a small amount of liquid in the bottom. Reduce heat to Low, and continue cooking for 2 to 4 hours, or until meat is totally tender and falls apart.
I usually substitute a can of diced green chiles for the peppers and use less hot sauce.