Beat together butter and sugars until light and fluffy.
Beat in egg and vanilla.
Combine flour, baking soda, salt and cinnamon and add to butter mixture, mixing well.
Stir in the oats.
Press dough into the bottom of a 9x13 ungreased baking pan, making sure to press firmly.
Bake for 20 minutes or until the crust is golden brown.
Cool completely in pan on a wire wrack.
Cut into squares.
You might want to add - raisins, chopped nuts, coconut, craisins, chocolate chips or peanut butter chips. For cookies - Drop by rounded tablespoon onto a greased cookie sheet. Bake 8-9 minutes. Cool on cookie sheet 1 minute. Remove to wire cooling rack.