1Heat oven to 350°F. Spray 8-inch square (2-quart) glass baking dish with cooking spray. In large bowl, stir sliced plums, 1/2 cup of the sugar and the cornstarch until combined. Spread in baking dish.
2In medium bowl, mix cookie crumbs, walnuts, Bisquick mix, butter and remaining 1/4 cup sugar with fork until crumbly. Sprinkle over plum mixture.
3Bake 45 to 55 minutes or until mixture is hot and bubbly and topping is lightly browned. Serve warm.