Preheat the oven to 350°F. Spread pecan pieces in a single layer on a baking pan. Toast for 6-8 minutes, then set aside to cool.
In a medium bowl use a whisk to sift together cake mix, oats and cinnamon.
Cut the cold butter into the dry ingredients using a hand mixer, food processor, or by hand using a pastry blender. Continue until all of the butter is incorporated and the mixture is crumbly. Separate out 1 cup and keep chilled.
Press the remaining mixture into an 13x9 inch non stick metal pan that has been sprayed with a baking spray.
Bake for 15 minutes until the edges begin to brown.
Meanwhile, using an electric mixer whip together dulce de leche, evaporated milk, egg and salt.
Remove crust from oven and layer the pecans, toffee bits and coconut over the crust. Drizzle the caramel filling evenly on top.
Crumble reserved 1 cup streusel on top and place back into the oven. Bake for 35-40 minutes until golden.
Cool completely in the pan on a baking rack before cutting.
Store in an airtight container at room temperature for up to 4 days.
Notes
If you're unable to find caramel cake mix you can adapt this recipe using butter pecan or yellow cake mix with no other adjustments needed.
Dulce de Leche is a luscious thick caramel. It's readily available at most grocery stores in the Hispanic foods section or at World Market and Williams Sonoma.