Preheat oven to 350 degrees Fahrenheit and butter or grease mini muffin pan. Set aside.
In a large bowl, whisk together flour, chia seeds, baking powder, baking soda, and salt. Set aside.
In a separate bowl, add sugar, egg, milk, butter, and lemon zest. Mix until fully combined. Add wet mixture to dry mixture and stir until just combined.
Fill mini muffin tins halfway with batter. Bake for 12-14 minutes, or until a toothpick inserted in the middle comes out clean (or with crumbs, not batter).
Allow pan to cool for 5 minutes before removing muffins from pan. If needed, use a butter knife around the edges of the pan to loosen your muffins. Allow to cool completely before storing in a sealed container.
This recipe will make 24 mini muffins, or about 8 standard sized muffins. If making standard size muffins, bake for 18-22 minutes, or until a toothpick inserted in the middle comes out clean.
Muffins will keep at room temperature in a sealed container for 3 days.
Baked muffins can be stored in the freezer for up to 3 months, tightly wrapped in foil and stored in a freezer safe container.