In a large mixing bowl, combine the oats, rice cereal, cashews, and dark chocolate. Melt the butter in the microwave or in a small pan over medium heat. When melted, immediately stir in the brown sugar, honey, vanilla, and salt. Pour the liquids over the dry ingredients and stir until evenly combined. Firmly press the mixture into the prepared pan. Bake until golden brown on the top, 18-20 minutes. Cool for 10 minutes and slice into bars.