1. In a medium saucepan, bring water to a boil and gradually stir in couscous.
2. Remove from heat, cover and let stand 5 minutes; fluff with a fork, cool.
3. Combine buttermilk, and next 6 ingredients in a large bowl; stir well with a whisk.
4. Add couscous, bell pepper, onions, and cucumbers; toss gently.