Coffee Cake

2 tablespoons canola oil, plus more for pan
4 cups all-purpose flour, plus more for dusting pan
1/2 cup granulated sugar
2 1/2 teaspoons baking powder
1/2 teaspoon salt
1 large egg
1/2 cup milk
2 teaspoons pure vanilla extract
1 cup light-brown sugar, firmly packed
1 1/2 teaspoon ground cinnamon
1 cup (2 sticks) unsalted butter, melted and cooled
Confectioners