First, go make the 2-Ingredient Vegan Caramel Sauce. You can even make this the day before if desired. Preheat the oven to 350 degrees F and line a 9-inch square baking dish with parchment paper (or simply grease the pan well). You can use an 8-inch pan for thicker bars.
In a large mixing bowl, stir the flour, oats, brown sugar, baking soda and salt together. Pour in the melted vegan butter and stir to form moist crumbs.
Press half of the crumbs on the bottom of the prepared pan, evenly and firmly. Bake for 10 minutes, then remove from oven.
Sprinkle the chocolate chips (and pecans, if using) over the warm crust, evenly.
For the caramel - If you have made this ahead of time and it's very thick, warm it for 30 seconds or so in the microwave until it's pourable. Pour the caramel over the chocolate chips.
Sprinkle the rest of the flour-butter crumb mixture on top of the caramel, and place in the oven. Bake for 15-20 minutes, until light golden brown and bubbling along the edges.
Cool on a rack for 20 minutes, then place in the refrigerator to chill for a few hours, if possible. They are still good before then, but they will fall apart easily and be very gooey. For firmer bars, chill for at least 4 hours.
Lift out using the parchment paper, slice into squares with a heavy knife, and serve.