Preheat oven to 350 degrees F. Line a 9x9 inch baking pan with parchment paper and spray with cooking spray.

Combine flour with baking powder, salt, and baking soda. Set aside.

In the bowl of a stand mixer, combine butter and sugar and beat together until light and fluffy, about 5-6 minutes.

Add eggs one at a time, fully incorporating the egg before adding another. Add lemon juice, vanilla, and oil, stirring until combined.

Add half of flour mixture, stirring just until combined. Add buttermilk then the remaining flour mixture, stirring just until combined. Stir in lemon zest and poppy seeds. Pour cake batter into prepared pan and bake for 40-45 minutes or until a toothpick inserted in the center comes out clean. Remove cake from oven and let cool completely on wire rack.

Make chocolate lavender ganache. Heat heavy cream with lavender over medium heat just until it starts to simmer. Remove from heat and add chocolate, stirring until melted. Let cool slightly for 10 minutes.

Cut cake into three even layers. Spread half of ganache evenly on bottom cake layer, then place a cake layer on top. Spread remaining ganache and place top cake layer on top, gently pressing down.

Make lemon cream cheese frosting. Beat together cream cheese with butter until light and fluffy. Add powdered sugar and beat until well combined. Add lemon juice and beat until well combined. Spread frosting on the top cake layer and sprinkle poppy seeds on top. Garnish with candied lemon rind if desired. Slice into 10 bars and serve.