Heat the sugar and water in a medium pot over medium-high heat. When the mixture reaches a bubble, reduce the heat to medium-low and add the ginger, plums and five-spice powder. Simmer for 10 minutes, then stir in the lemon juice. Remove from the heat and let cool for about 5 minutes. Add the plum mixture to a blender or food processor and process until smooth. Pour into a medium bowl and stir in the hoisin sauce. Reserve.
While the plums are cooking, put the pork tenderloins on a sheet pan and coat with oil, grill seasoning and coriander. Grill, or broil 6 inches from heat, until just firm, about 20 to 22 minutes. Remove from the grill to a cutting board and tent with foil. Let rest for about 5 minutes, then slice and arrange on a platter. Top with the plum barbecue sauce and serve.