Trim fat from meat. Cut the meat into ½-inch pieces. Cook half of the meat in a large skillet in hot oil over medium-high heat until browned. Using a slotted spoon, remove the meat from the skillet. Repeat with the remaining meat and the onion. Drain off fat. Transfer all of the meat and the onion to a 3 ½- to 4 ½-quart slow cooker.
Stir in potatoes, the water, hominy, green chile peppers, tapioca, garlic salt, cumin, ancho chile powder, ground pepper, and oregano. Cover and cook on Low for 7 to 8 hours or on High for 4 to 5 hours. If desired, garnish each serving with cilantro.
