Preheat and prep: Heat the oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease with oil.
Mix dry ingredients: In a large bowl, whisk 1 cup oat flour, 1/2 cup all-purpose flour, 1/2 cup chocolate or vanilla protein powder, 1/3 cup unsweetened cocoa, 1 1/2 tsp baking powder, 1/2 tsp baking soda, 1/2 tsp fine sea salt, and 1 tsp espresso powder.
Blend wet ingredients: In a separate bowl, whisk 3/4 cup Greek yogurt, 2 large eggs, 1/2 cup milk, 1/4 cup avocado oil, 1 tsp vanilla, 1/3 cup honey or maple, and 1/4 cup brown sugar until smooth.
Combine: Pour the wet mixture into the dry. Stir gently until just combined.
The batter will be thick—avoid overmixing.
Fold in chocolate chips: Add 1/2 cup mini dark chocolate chips. Fold a few times to distribute evenly.
Portion: Divide the batter among the 12 muffin cups. For extra chocolate, sprinkle a few more mini chips on top.
Add a pinch of flaky sea salt if you like contrast.
Bake: Bake 15–18 minutes, or until the tops spring back lightly and a toothpick comes out with a few moist crumbs (a little melted chocolate is okay).
Cool: Let muffins rest in the pan for 5 minutes, then transfer to a wire rack to cool completely. This helps set the texture and prevents sogginess.