In a small saucepan bring the water to a boil. Add the rhubarb and blanch (10 secs). Remove and immediately dip into cold water just long enough to freshen.
Remove and let drain briefly. Finely dice the rhubarb and set aside. Seed and devein the pepper. Starting on the long side, finely chiffonade the pepper into threads. In a medium bowl combine 2 cups rhubarb, the pineapple, onion and pepper. Pour the lemon juice over the mixture and toss. Add the brown sugar and salt. Gently stir in the cilantro. Refrigerate.