Combine oats, flour, 3/4 cup brown sugar, 1/2 cup chopped pecans, 1/2 teaspoon salt, the baking soda, and the butter; beat until mixture is crumbly. Reserve about 1 1/2 cups of the crumb mixture and press remaining mixture into a lightly buttered 13x9x2-inch baking pan. Bake at 375° for 10 minutes.
Prepare filling. Beat filling ingredients until well blended and smooth. Spread filling over the crust; sprinkle with remaining crumb mixture. Return to oven and bake 25 minutes longer. Cool and cut into bars.
*The following can be combined to make pumpkin pie spice
1 1/2 teaspoons ground cinnamon
3/4 teaspoon ground ginger
1/4 teaspoon ground nutmeg
1/4 teaspoon ground allspice
My Notes: I pretty much followed this recipe to the T, including the pumpkin spice substitute! One thing I did do.... I beat the egg really good before I put it into the puree... to ensure that I didn't have pieces of egg in my bars! I chose to use pecans because that what I had in the house! These came out absolutely delicious! My husband actually said he liked this better than pumpkin pie!!! The bars are a bit soft like pumpkin pie so I would keep the bars in a pan until it is time to serve, instead of transferring them onto a serving plate. The topping/crust was a hit! Very very good!!! I would suggest making a little extra topping! I ran out and couldn't cover as much of the squares as I would have liked... but still delicious!