Combine quartered figs brown sugar lemon zest kosher salt and vanilla extract in a medium heavy-bottom saucepan Cook over medium heat until the figs begin to release juices and mixture comes to a gentle boil Reduce heat and simmer for 45 minutes stirring occasionally and mashing pieces with a wooden spoon Remove from heat and allow to cool For a smooth consistency puree filling using an immersion blender blender or food processor
Preheat oven to 350°F Line a 9×13-inch baking pan with aluminum foil allowing overhang on sides and coat with nonstick cooking spray In a large microwave-safe bowl melt the butter Add flour rolled oats brown sugar salt baking powder and vanilla extract Stir until well blended ensuring no streaks of flour remain mixture will be thick and may be easier to mix by hand
Reserve 1 1/2 cups of oat mixture Press remaining oat mixture evenly into the prepared pan to form a base using the bottom of a glass to compact firmly Spread cooled fig filling evenly over the base Crumble reserved oat mixture over the fig layer
Bake on the center rack for 30 to 35 minutes or until the fig filling is bubbling and the top crumble is golden brown Remove from oven and cool completely in the pan Use foil overhang to lift the entire slab from the pan then slice into bars for serving
Notes
For neat slices chill the assembled bars before cutting with a sharp knife