Line a 9x13" pan with parchment paper or foil; spray with cooking spray. Preheat your oven to 350°.
Combine the flour, oats, brown sugar, soda, salt, vanilla, and butter in a large bowl. Mix with your fingers or a fork until crumbly.
Press about 2/3 of the crumbs into the bottom of the prepared pan. Spread the jam evenly on top. Sprinkle the rest of the crumble topping over the jam. (It's fine if some of the jam shows through.)
Bake the bars at 350 degrees for about 45 minutes, or until the topping is golden brown.
Let cool for at least an hour, but for the cleanest slices, let cool for two hours. You can chill the bars to speed up the process.
Hold the ends of the parchment and lift the bars out of the pan and onto a cutting board. Cut into squares or triangles with a long, sharp knife.
Notes
It is much easier to press the parchment into the pan if you first crumple it up.
I like to bake my bars on a lower oven rack to the bottom crust browns before the top gets too brown.
I cut my bars about 2 1/4", but you can cut them larger if you want.
Bars can be stored in an airtight container for up to a week. You can also freeze them for 3-4 months. For best results, first wrap them in plastic wrap, then transfer to a heavy duty ziplock bag or freezer-safe container.
*Quick oats tend to have a floury coating, which can make the bars dry. If you use quick oats, cut the flour down by a couple tablespoons.