Preheat the oven to 160 C degrees. Grease and line an approx. 22x22cm baking tray.
Mix the flour, oats, sugar, salt and cinnamon, then rub the butter in using your fingers until you get a coarse crumble.
Tip half of the mixture into the prepared tin, then spread it out evenly, pressing down slightly with the base of the spoon.
Spread some jam on top evenly - as thickly as you like - then add the remaining oat mixture. Again, spread it out evenly, while lightly pressing down.
Bake the cake for about 45 minutes until golden brown. Let it cool in the tin, then move it to a wire rack.
When completely cooled, slice it into squares or bars.