In a mixing bowl, place oil, sugar, eggs, 3 cups flour, baking powder, orange juice and vanilla. Mix cake batter with a mixer on high speed .
In a separate bowl, create a cinnamon mixture by combining cinnamon, cocoa and brown sugar.
In a 3rd bowl, make a crumb mixture by combining 1/2 cup of flour with sugar and margarine softened at room temperature. Mix by hand till it becomes crumbs.
In a 9x13"-inch pan, layer cake batter, cinnamon mixture, cake batter, cinnamon mixture and then crumb mixture on top. Bake at 350*F for about 60 minutes.