Heat oven to 425°F. Spray 9-inch round cake pan with cooking spray. In 2-quart saucepan, heat rhubarb, 1 cup sugar and 1 tablespoon water to boiling over medium-high heat. In small bowl, mix cornstarch and 2 tablespoons cold water; stir into rhubarb mixture. Reduce heat to low; simmer uncovered about 5 minutes, stirring occasionally, until rhubarb is tender. Cool sauce about 30 minutes. Stir in strawberries.