1Heat oven to 375°F. In medium bowl, mix butter, brown sugar and vanilla with spoon. Stir in 2 cups flour, the oats, nuts, baking soda and salt until crumbly. Reserve 2 cups crumbly mixture. Press remaining crumbly mixture in ungreased 15x10x1-inch pan.
2In large bowl, mix granulated sugar, 2/3 cup flour, the milk and eggs with spoon until smooth. Fold in strawberries and rhubarb. Spoon filling onto crust. Sprinkle with reserved crumbly mixture.
3Bake 40 to 50 minutes or until topping is golden brown and filling is set. Cool slightly, about 30 minutes. For serving pieces, cut into 5 rows by 4 rows. Serve with whipped cream. Store covered in refrigerator.