1. For filling, in a medium bowl, zest one lemon before juicing all three. Remove seeds as necessary.
2. Add the remaining filling ingredients. Whisk until well combined, then pour the filling into the crust. Bake 23-28 minutes or until set.
3. Remove pan from oven and allow bars to cool for at least 10 minutes.
4. Carefully lift the bars from the baking dish by the parchment and allow to cool completely on a wire rack.
5. Dust the top with Powdered Swerve (or powdered sugar), slice, and serve.