Preheat oven to 375°.
Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and the next 4 ingredients (flour through brown sugar) in a medium bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal.
Combine rhubarb, 2/3 cup granulated sugar, and cornstarch in a large bowl, tossing to coat. Spoon rhubarb mixture into an 11 x 7-inch baking dish coated with cooking spray. Drop strawberry spread by spoonfuls over rhubarb mixture; sprinkle with oats mixture. Bake at 375° for 40 minutes or until browned and bubbly.