Heat the oil in a large pot over medium-high heat. Add the popcorn kernels and cover the pot. Once the kernels start to pop, shake the pot occasionally to ensure even popping.
In a medium saucepan, melt butter over medium heat. Add brown sugar, corn syrup and cinnamon, stirring until sugar is dissolved.
Pour caramel mixture over popcorn and stir until evenly coated. Transfer to a large baking sheet and bake at 350°F for 5 minutes.