1. Bring 2 1/4 cups water and barley to a boil in a saucepan. Cover, reduce heat, and simmer for 25 minutes or until tender and liquid is almost absorbed. Cool to room temperature.
2. Combine lemon rind, lemon juice, olive oil, and mustard in a bowl; stir well with a whisk. Add barley, fennel, and next 6 ingredients (through beans); toss gently. Cover and refrigerate for 30 minutes. Garnish with walnuts just before serving.