Preheat oven to 225ºF. Spray a 15 x 10-inch baking pan with cooking spray.
Combine popcorn and nuts in baking pan and place in oven to keep warm.
Heat chocolate, brown sugar, corn syrup and butter in a 2-quart saucepan over medium heat until boiling, stirring occasionally
Boil 5 minutes, stirring constantly.
Remove from heat and immediately stir in baking soda.
Pour chocolate-caramel mixture carefully over popcorn and nuts.
Use cooking spray-coated tongs or a spatula to toss the popcorn and chocolate-caramel mixture.
Bake popcorn for 60 minutes stirring popcorn about halfway through.
Let popcorn cool completely on wire rack.
Break popcorn into bite-sized pieces and store in an airtight container.