Preheat oven to 350°F (175°C). Line an 8×8-inch pan with parchment paper, leaving overhang for easy removal.
Make the crust/crumble mixture. In a large bowl, stir together flour, oats, brown sugar, baking soda, and salt. Add melted butter and vanilla. Mix until crumbly.Press about 2/3 of the mixture firmly into the bottom of the pan to form the crust. Set aside the rest for the topping.
In a medium bowl, mix strawberries, cornstarch, lemon juice, and sugar until well combined.
Spoon the strawberry mixture evenly over the crust. Sprinkle the remaining oat mixture over the top.
Bake for 30–35 minutes, or until the top is lightly golden and the strawberries are bubbling.
Let bars cool completely in the pan. Chill for firmer bars. Slice and enjoy!