Combine first three ingredients in a medium saucepan; bring to a boil. Reduce heat, and simmer, uncovered, 5 minutes or until rhubarb is tender. Combine 1 tablespoon water and cornstarch; stir well, and add to rhubarb mixture. Bring to a boil, and cook 1 minute or until thickened, stirring constantly. Remove from heat; stir in strawberries and vanilla. Serve warm or chilled over angel food cake, sponge cake, or vanilla low-fat ice cream.