Preheat the oven to 350. Line a 9x13 inch baking dish with parchment; set aside.
Mix oats, flour, brown sugar, baking powder, salt and butter into a crumb-like mixture. Press 2/3 of the mix into an even layer in your prepared baking dish. Bake in the oven for 10 minutes.
Meanwhile, add fresh raspberries to a medium bowl. With the back of a wooden spoon or masher, press the berries until partially smashed with some big bits. Mix in the sugar, jam and zest. Sift in the flour and corn starch and stir.
Arrange the raspberry layer on the baked bottom layer. (You can do this with the bottom still hot from the oven.) Sprinkle the remaining crumble over top of the berries. Place back into the oven and bake for another 25 -30 minutes, until crumble is lightly brown and berries are slightly bubbly.
Sprinkle the warm top with thyme. Allow to cool on the counter and then chill in the refrigerator so they will cut easily into bars, about 2 hours. Lift parchment from pan and cut into squares.