Place 2 Tbsp of vegetable oil and one popcorn kernel in a large pot over high heat with a lid. Wait for the kernel to pop then add the rest of the 1/2 cup of kernels. Swirl the kernels in the pot to coat them with oil and then wait for them to pop. When the popping slows (just like with microwave popcorn) remove it from the heat. I like to keep the lid slightly ajar as they pop to let steam out but keep the jumping kernels in.
In a small pot, combine the water, sugar, butter and salt. Place the pot over medium heat and let the mixture come to a boil. Continue to boil the mixture until it is a light gold color (see photos below).
While the sugar mixture is boiling, remove any unpopped kernels from the popcorn and add the nuts. Line a large baking sheet with foil and spray with non-stick spray. Preheat the oven to 250 degrees.
Once the sugar mixture becomes golden, remove it from the heat and stir in the baking soda and spices (cayenne, chili powder or none). Immediately pour the mixture over the popcorn and nuts and stir to combine. Work quickly as you stir because the mixture will harden as it cools. Pour the popcorn/nut/sugar mix out onto the baking sheet, place in the oven and bake for about 15 minutes. Let the mix cool for 5-10 minutes before eating to let the caramel sauce harden.