Set oven to 350 F/ 175 C and prepare a parchement-lined square baking pan.
Combine raspberries, lemon juice, sugar, corn starch, and vanilla extract in a mixing bowl. Stir properly.
Add into another mixing bowl rolled oats, flour, baking powder, brown sugar, salt, cinnamon powder and cubed butter.
Combine all ingredients together with clean hands, mixing thoroughly till the butter is well incorporated into the dough and there are no more visible lumps.
Pour mixture into a parchment-lined baking pan and push the dough down making sure it is even and flat.
Pour over the raspberry filling. It may have started breaking down by now but make sure to pour everything along with the juices on top of the crust layer.
Even the raspberry filling out with a spatula or spoon.
Lastly, sprinkle the remaining oatmeal dough all over the top of the raspberry filling to cover it.
Bake for 25 minutes in a 350 F/ 175 C preheated oven.
Let it cool down in the pan for an hour, then transfer it to cool down further in the fridge for another hour.
Gently lift out of the baking pan, set on a chopping board, and cut into the desired number of squares or bars. Serve.