Preheat your oven to 350°F (175°C) and grease an 8x8-inch baking pan.

In a large mixing bowl, combine rolled oats, whole wheat flour, and baking powder. Add lemon zest if desired.

In a separate bowl, whisk together eggs, honey (or maple syrup), and melted butter (or coconut oil) until frothy.

Gently fold in the blueberries into the wet mixture, making sure not to smash them.

Pour the wet mixture into the dry ingredients and stir gently until just combined.

Transfer the batter to the greased baking pan, smoothing the top. Bake for 35-40 minutes.

Allow the bars to cool on a wire rack for 15-20 minutes before cutting.

Store the bars in an airtight container at room temperature for up to 3 days or in the fridge for a week.