1Cut beef into 1- to 1 1/2-inch pieces. Heat oil in 12-inch skillet over medium-high heat. Cook beef in oil, in batches if necessary, 8 to 10 minutes, turning occasionally, until brown on all sides.
2Place beef in 3- to 4-quart slow cooker. Sprinkle with garlic, oregano, 1 1/2 teaspoons salt, the pepper and 3 tablespoons of the lemon peel; toss to mix.
3Cover and cook on Low heat setting 4 to 5 hours.
4Stir together yogurt, cucumber, 1/2 teaspoon salt and remaining 1 tablespoon lemon peel in small bowl. Serve beef with toothpicks for dipping into yogurt sauce. Beef bites will hold on Low heat setting up to 2 hours; stir occasionally.