For the crust, preheat the oven to 350°F. Butter a 9 by 13‑inch baking dish with the softened butter; set aside.
For the crust, combine the graham cracker crumbs, oats, brown sugar, melted butter, and milk in a medium bowl. Press the mixture evenly into the bottom of the prepared baking dish. Bake for 10 minutes or until lightly golden brown.
For the filling, combine the pumpkin, eggs, granulated sugar, yogurt, milk, cinnamon, pumpkin pie spice, and salt; mix until thoroughly blended. Pour the filling into the baked crust and spread evenly. Bake for 30 minutes or until the filling is almost set.
Sprinkle the pecans evenly over the filling and bake for 10 to 15 minutes more or until the center is set. Transfer the dish to a wire rack to cool completely.
For the topping, mix the yogurt, granulated sugar, and cinnamon in a small bowl; cover and chill until ready to serve.
To serve, cut into squares. Top each square with a dollop of yogurt topping.