Preheat oven to 350°F (175°C). Line a 13×9-inch baking pan with parchment paper, leaving a 1-inch overhang on the sides.
In a large bowl, combine flour, oats, brown sugar, baking soda, and salt. Stir in melted butter until mixture forms a coarse crumble.
Press two-thirds of the oat mixture evenly into the prepared pan.
Sprinkle chopped pecans, semisweet chocolate chips, and chopped baking chocolate over the crust.
In a small saucepan over low heat, melt the caramels with heavy cream, stirring constantly until smooth.
Pour caramel mixture evenly over the chocolate and nuts.
Crumble the remaining oat mixture over the caramel layer.
Bake for 23 minutes, or until the top is lightly golden.
Cool completely in the pan on a wire rack.
Lift bars out using the parchment overhang, then cut into squares.
Optional: melt remaining caramels and chocolate chips separately, then drizzle over cooled bars.