Preheat oven to 375°. Line an 8-inch square baking pan with foil, letting excess extend over sides of pan. Spray with baking spray with flour.
In a large bowl, beat flour, 1 cup sugar, oats, butter, vanilla, and salt with a mixer at medium-low speed until mixture is crumbly. Press 1¼ cups mixture into prepared pan.
In another large bowl, combine strawberries, rhubarb, cornstarch, lemon juice, and remaining ½ cup sugar. Pour fruit mixture over crust. Sprinkle with remaining crumb mixture.
Bake until browned and bubbly, 45 to 55 minutes. Let cool completely on a wire rack. Using excess foil as handles, remove from pan, and cut into bars.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/strawberry-rhubarb-crumble-bars/