In a medium pot, add the halved figs, 1/3 cup brown sugar, lemon zest, 1/4 tsp salt, 1 1/2 tsp vanilla essence, and ground cinnamon. Heat over medium until the mixture reaches a boil, then lower the heat and let it simmer for approximately 45 minutes. Stir occasionally and press the figs against the pot's side to break them down into a chunky paste. When the mixture becomes thick and deeply jammy in texture, take it off the heat and allow it to cool for 10 minutes.

Using an immersion blender or food processor, blend the cooled fig mixture until it's completely smooth. This creates a filling that spreads evenly and contrasts nicely with the crumbly crust. Set it aside to cool to room temperature while you work on the base.

Heat your oven to 350°F. Line a baking pan with foil and apply a light coating of grease to prevent sticking. In a large mixing bowl, stir together the melted butter, flour, old fashioned oats, 1 cup brown sugar, 3/4 tsp salt, baking powder, and 1 tbsp vanilla essence. Combine until the mixture looks like coarse breadcrumbs with some larger oat pieces scattered throughout.

Reserve 1 1/2 cups of the oat mixture and set it aside. Take the remaining mixture and press it firmly and evenly into the bottom of your prepared pan to form the base layer. Spread the completely cooled fig filling over this base, keeping about 1/4 inch away from the edges. An offset spatula works well for spreading the filling uniformly without disrupting the crust underneath. Take the reserved 1 1/2 cups of oat mixture and crumble it over the filling in an uneven, rustic pattern, making sure some areas have thicker clusters for varied texture.

Place in the preheated 350°F oven and bake for 30 to 35 minutes, until the top turns light golden brown and the filling feels set but remains slightly soft when pressed gently. Allow the bars to cool completely in the pan for a minimum of 30 minutes to ensure they set properly. Use the foil edges to lift the entire sheet out of the pan, peel the foil away carefully, and transfer to a cutting board. Cut into even bars using a sharp knife, cleaning the blade between each cut for neat, clean edges.