Preheat the oven to 180°C (350°F) and line a muffin tray with paper cases.
In a bowl, whisk together the buckwheat flour, almond flour, baking powder, salt, sugar, cinnamon, and chia seeds.
In another bowl, whisk the yogurt, eggs, melted butter, and vanilla extract until well combined. Stir in the mashed banana and grated apple.
Add the wet ingredients to the dry ingredients and fold until just combined. Gently stir in the chopped chocolate.
Divide the batter evenly among the muffin cases. Bake for 25 minutes or until the tops are golden brown. Let the muffins cool in the tray for a few minutes before transferring them to a wire rack to cool completely.
