Preheat the oven to 300 degrees F. Line a baking sheet with a piece of parchment paper and spray lightly with cooking spray.
Put the oil and 3 or 4 popcorn kernels in a large pot with a lid (at least 6 quarts). Cover the pot and turn the heat up to medium-high. Wait until you hear one of the kernels pop, then uncover the pot and add the remaining kernels. Quickly stir everything together then replace the lid. Cook the popcorn until the kernels begin popping and then reduce the heat slightly. Cook, shaking often, until the rate of popping starts to slow, 2 to 3 minutes. Do not wait for all of the kernels to pop or they will burn. Take off the heat.
Combine the brown sugar, corn syrup, butter and salt in a medium pot. Heat over medium heat until melted and smooth. Stir in the baking soda.
Pour the nuts on top of the popcorn. Then pour the caramel into the pot with the popcorn; stir to coat and spread the popcorn onto the prepared baking sheet.
Bake, stirring occasionally, until slightly golden, about 20 minutes. Cool completely, and then break apart before serving.