Cream butter and sugar. Add flour and oatmeal to make a crumbly dough. Set aside.
In another bowl, add sweetened condense milk, lemon juice and peels. Mix well. In a buttered 9x13 pan, press 3/4 of the dough into the pan. Pour sweetened condensed milk mixture over the dough. Sprinkle the remaining dough over the top of the entire mixture so that it resembles streusel.
Bake at 350 degrees for 30 minutes or until golden.