In a dry skillet over medium-high heat, cook walnuts until lightly toasted, about 1 to 2 minutes; set aside and reserve. In large bowl, combine boiling water, couscous, garlic and gingerroot. Cover, let stand 5 minutes. With a fork, fluff couscous; chill 15 minutes.
Stir in yellow pepper, cucumber and radishes. In small bowl, combine orange juice, vinegar, cumin, cayenne pepper and salt and pepper. Pour over salad; toss well. Garnish with cilantro.