FOR THE FILLING: Adjust oven rack to middle position and heat oven to 375 degrees. Toss all ingredients in large bowl until thoroughly combined. Transfer to 10-inch oven safe skillet. Cook over medium-high heat, stirring frequently, until fruit has released enough liquid to be mostly submerged, rhubarb is just beginning to break down, and juices have thickened, about 8 minutes. Remove skillet from heat.