In a bowl, combine condensed milk, sour cream, lemon juice, and vanilla. Mix well, and then chill.
In a large bowl, beat butter and sugar until fluffy. Add flour, oats, and nuts. Mix well. Press on a lightly greased pizza pan. Form a rim around edge. Prick with a fork. Bake 10-12 minutes. Cool. Pour filling evenly over crust. Arrange fruit on top. Chill.
SUGGESTED FRUIT: Strawberries, kiwi, grapes, pineapple, mandarin oranges, or any fruit in season.