In a saucepan, combine rhubarb, water, honey, hoisin, garlic, ginger, 5-spice powder & crushed red pepper. Bring to a simmer; cook, stirring occasionally, until slightly reduced & the rhubarb is very soft, about 10 minutes. Remove from heat & stir in soy sauce & lemon juice. Transfer 2 TABLESPOONS of the sauce to a saucer; set aside the remaining sauce until serving time.