Place a 12-inch square of foil on a baking sheet, and spray the foil with nonstick vegetable spray. Heat the brown sugar, olive oil, and balsamic vinegar in a large skillet over medium heat, stirring, until the sugar melts and the mixture bubbles. Add the pecans and the cayenne, and stir until the nuts are well coated. Transfer the nuts to the foil, spreading them out, and allow them to cool completely (they will harden and dry).