Preheat the oven to 350°F. Line an 8×8 pan with parchment paper or spray with oil.
Make filling: Gently toss raspberries with sugar, lemon juice, and cornstarch.
Make oat mixture: In a large bowl, mix oats, flour, brown sugar, baking soda, and salt. Stir in melted butter and vanilla until crumbly.
Press crust: Firmly press ⅔ of the oat mixture into the pan.
Add filling: Spread raspberries evenly over the crust.
Top: Sprinkle remaining oat mixture over the berries.
Bake for 35–40 minutes, until golden and bubbling.
Cool completely before cutting into bars.