Preheat the oven to 225°. Spray a large baking sheet with cooking spray. In a skillet, cook the bacon over medium-high heat until crisp; drain and coarsely chop. In a bowl, combine the popcorn and bacon.
In a saucepan, cook the brown sugar, butter and corn syrup over low heat, stirring, until the sugar dissolves. Increase the heat to medium and simmer, stirring, for 4 minutes. Remove from the heat; stir in the baking soda. Stir in the nuts.
Pour the nut mixture into the popcorn mixture, stirring to coat. Spread the mixture in an even layer on the prepared baking sheet. Bake for 45 minutes. Let cool completely.