Combine the halved figs, 1/3 cup brown sugar, lemon zest, 1/4 tsp salt, 1 1/2 tsp vanilla essence, and ground cinnamon in a medium pot. Bring to a boil over medium heat, then reduce heat and simmer for about 45 minutes, stirring occasionally and mashing the figs against the side of the pot until they break down into a chunky paste. Once the mixture is thick and deeply jammy, remove from heat and let cool for 10 minutes. Blend the cooled fig mixture until completely smooth using an immersion blender or food processor—I find a smooth filling spreads more evenly and creates a better texture contrast with the crumbly oat crust. Set aside to cool completely while you prepare the base.

Preheat your oven to 350°F. While the fig filling cools, prepare your baking pan by lining it with foil and lightly greasing it—this makes it incredibly easy to lift the finished bars out cleanly. In a large bowl, combine the melted butter with the flour, old fashioned oats, 1 cup brown sugar, 3/4 tsp salt, baking powder, and 1 tbsp vanilla essence. Mix until the ingredients are evenly distributed and the mixture resembles coarse breadcrumbs with some slightly larger oat clusters remaining.

Press all but 1 1/2 cups of the oat mixture from Step 2 firmly into the bottom of your prepared pan, creating an even layer. Spread the cooled fig filling from Step 1 evenly over the base layer, leaving about 1/4 inch from the edges. I like to use an offset spatula for this so the filling stays uniform without creating holes in the crust below. Crumble the reserved 1 1/2 cups of oat mixture over the top, distributing it unevenly for a rustic appearance and ensuring some spots have thicker clusters for textural contrast.

Bake at 350°F for 30-35 minutes, until the top crust is light golden brown and the filling is set but still slightly soft when gently pressed. Let the bars cool completely in the pan for at least 30 minutes so they set properly. Lift the entire sheet from the pan using the foil edges, then carefully peel back the foil and transfer to a cutting board. Slice into even bars with a sharp knife, wiping the blade between cuts for clean edges.