Combine rhubarb and lemon zest in 1-pint glass jar with tight-fitting lid. Combine sugar, water, vinegar, and salt in small saucepan and bring to boil over medium-high heat. Pour brine into jar, making sure all rhubarb is submerged. Let cool completely, about 2 hours.
Affix jar lid and refrigerate for at least 24 hours before serving. (Pickles can be refrigerated for up to 2 weeks.)
