Preheat the oven to 350F.
In a medium bowl, combine the flour, oats, brown sugar, baking soda and salt. Add the butter and blend with a fork or your fingers until the mixture is well combined and crumbly.
Press a little more than half into the bottom of a parchment-lined 8x8-inch pan, spread with the jam, and sprinkle the rest of the crumble mixture on top, squeezing a bit as you go to create larger clumps.
Bake for 40-45 minutes, until pale golden and the jam is bubbling around the edges. Cool before cutting or serve them warm, with vanilla ice cream. Makes 9-16 squares.