In a large mixing bowl, combine oil, eggs, vanilla and milk. Add sugar, flour, baking powder and salt.
Pour half of the batter into a 9x13 baking pan.
In a small bowl, combine brown sugar and cinnamon. Sprinkle half of streusel on top of batter. Top with remaining batter and sprinkle the remaining streusel on top. Drizzle with melted butter.