Preheat oven to 350° F. Line an 8-inch square baking dish with parchment paper, allowing extra paper to extend over the sides of the pan. Spray parchment with baking spray.
In a large bowl, stir together flour, oats, pecans, brown sugar, cinnamon, salt and baking soda. Add melted butter and stir until the mixture is crumbly.
Reserve 1 cup of the flour mixture. Press the remaining flour mixture into the bottom of the prepared pan.
Spread the raspberry preserves onto the crust in the pan. Sprinkle the reserved flour mixture over top, squeezing together with your hands to make clumps.
Bake until golden brown, about 50-55 minutes.
Let cool in the pan for 20 minutes, then refrigerate until firm (at least 1 hour).
Notes
Use old-fashioned rolled oats (not quick oats or "instant oats") for the best texture.
Chop the pecans fairly small. You don't want them in a fine powder -- texture is good! -- but they should be small enough that they don't cause the crust to fall apart.
Pick a high-quality brand of raspberry jam or preserves, since this is a key ingredient. I prefer Bonne Maman preserves.
Chill the bars before slicing. They need some time to cool in order to set up. If you cut into the warm bars, you'll have a crumbly mess rather than neat squares.