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.
To a medium-size mixing bowl, add the cake mix, oats and cinnamon. Sift together with a whisk.
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 13 x 9 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 or a whisk, whip together dulce de leche, evaporated milk, egg and salt.
Layer the pecans, toffee bits and coconut over the crust. Drizzle the caramel filling evenly on top.
Crumble reserved chilled streusal topping 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 3 days.