Mix onion, olive oil, vinegar, and seasoning. Pour over cucumber and add feta. Toss well. Mix the orzo, butter and cooking liquid, stirring until butter is melted. Add Romano cheese and mix gently. Divide orzo among the lettuce leaves and add a few strips of the steak. Top with the cucumber-feta mixture and garnish with tomato (optional). Serve immediately. Serves 4-6 (2 or 3 lettuce cups each)