Preheat the oven to 350℉. Line a 9X9-inch pan with parchment paper, leaving parchment paper to hang over the sides of the pan.

Combine the oats, flour, brown sugar, and baking powder in a medium-sized bowl. Pour in the melted butter and stir until crumbly but moist. Pour approximately ⅔ of the mixture into the prepared pan and press to form a crust. Set the remaining mixture aside for the topping later.

In another bowl stir together the raspberries, sugar, cornstarch, and lemon juice. Mash and muddle the raspberries until jammy looking. Pour the filling over top of the crust and spread it around. Crumble the remaining crust mixture over top.

Bake in the preheated oven for 30-40 minutes or until the filling is bubbly and the topping is golden. Let cool fully before serving as bars or serve it warm with ice cream (like a crisp).