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.
I've been making this for several years now and everyone loves it. I usually cut down the sugar a bit since I like my rhubarb tart. I usually serve it over angel food cake. Tried it with vanilla ice cream once, but didn't like it as well.