Preheat oven to 350°. In a small bowl, mix flour, oats and brown sugar; cut in butter until crumbly. Reserve 1 cup mixture for topping. Press remaining mixture onto bottom of a greased 9-in. square baking pan.
For filling, beat cream cheese, sugar, salt and spices until smooth. Add egg and vanilla; beat on low speed just until combined. Fold in rhubarb. Spread over crust. Sprinkle with topping.
Bake until golden brown and filling is set, about 40 minutes. Cool on a wire rack 1 hour. Refrigerate, covered, until cold, about 2 hours. Cut into squares