Combine bacon, tomato and greens with mayonnaise. Season with pepper; set aside.
Peel cucumber. Trim off ends, and slice in half lengthwise. Use a spoon to scoop out seeds; discard. Place cucumber in a glass dish. Divide BLT mixture between segments, mounding in hollowed areas. Sprinkle with minced parsley or green onion, if desired. Slice into 2-inch pieces.