In a medium bowl, combine cake mix, margarine, and one of the eggs until it makes a soft dough, then press it into the bottom of a greased 9x13" pan.
In a separate medium bowl, mix together the second egg, the sweetened condensed milk, and the vanilla until completely combined. Fold in the chopped pecans and the toffee bits. Pour this mixture over the crust in the 9x13" pan.
Bake for 25-30 minutes, until the bars start to turn a golden brown on top.
Notes
You can serve these hot out of the oven like a cobbler, or let them cool a little bit for cleaner-cut bars.