Preheat oven to 180 degrees C. Grease a 20x30cm baking dish.
In a saucepan over medium heat, melt the caramels with the evaporated milk, stirring frequently until smooth. Set aside.
In a medium bowl, stir together the flour, oats, brown sugar, bicarb soda and salt. Stir in the melted butter. Press half of the mixture into the bottom of the prepared pan.
Bake for 10 minutes in the preheated oven. Remove from the oven and sprinkle the crust with chocolate chips and walnuts. Drizzle the caramel mixture over all. Crumble the remaining oat mixture evenly over the top and pat down lightly.
Bake for an additional 15 to 20 minutes, or until the top is golden. Cool before cutting into bars.