1. Preheat broiler; broil lamb cubes on rack 4" from heat, 2 minutes.
2. In medium nonstick skillet, heat olive oil; add onion. Cook, stirring frequently, 2-3 minutes, until tender. Add lamb cubes, zucchini, mint and salt; cook, stirring frequently, 5-6 minutes, until zucchini is tender and lamb is done to taste.
3. Remove lamb mixture from heat; stir in yogurt and lemon juice. Spoon lamb mixture over orzo. Toss to mix well.