Combine flour, baking soda, and salt in a small bowl.
Beat butter, granulated sugar, and brown sugar at medium speed with a heavy-duty electric mixer 2 minutes or until well blended. Add egg and vanilla, beating until blended. Add oil, beating until blended. Add flour mixture, beating at low speed until blended. Add oats and next 3 ingredients, beating until blended.
Shape dough into 1-inch balls. Place on baking sheets, and flatten gently with tines of a fork.
Bake at 325° for 12 minutes or until edges are lightly browned. Remove to wire racks to cool completely. Sprinkle with powdered sugar.