Preheat the oven to 350°F.
To make the topping, first stir the flour, sugar, cinnamon, and salt together in a medium bowl. Cut the chilled vegan butter into slices and add it to the bowl, then use a pastry cutter or fork to cut the butter into the flour mixture, until the mixture resembles coarse crumbs. Stir in the pecans. Place the topping in the fridge to chill while you make the crust and filling.
To make the crust, stir together the flour, sugar, and salt in a large mixing bowl. Add the melted vegan butter and vanilla. Stir until a dough forms.
Press the mixture in an even layer into the bottom of a 9 x 13 inch baking pan.
Bake the crust until it's slightly puffy and darkened around the edges, 18 to 20 minutes.
Place the pan on a cooling rack when it comes out of the oven.
While the crust cools, make the filling. Place all of the filling ingredients into a large mixing bowl, then beat them together with an electric mixer at high speed, until blended and creamy, about 1 minute.
Spread the filling evenly over the crust (it's okay if it's still warm).
Sprinkle the topping evenly over the filling.
Bake the bars for about 45 minutes, or until the filling feels partially set but just a touch wobbly in the middle.
Let the bars cool completely. Slice and serve immediately, or chill for later.