Remove excess fat from meat. Cut meat into serving-size pieces. Use a large skillet and cook meat, half at a time, in hot oil over medium heat until brown (add more oil, if necessary). Drain off fat. Place onions in a 3 1/2- or 4-quart slow cooker. Add meat. Combine in a small bowl the coffee, soy sauce, garlic, bay leaves, and oregano. Pour over meat in cooker.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours.
Remove meat and onions to a serving platter, reserving cooking liquid. Cover meat and onions with foil to keep warm.
If using low-heat setting, turn to high-heat setting. Combine in a small bowl the cornstarch and water. Stir liquid into the cooker. Cover and cook for 15 minutes until thickened. Remove and discard bay leaves. Spoon some of the sauce over meat and onions. Pass remaining sauce.