Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or lightly grease each cup with cooking spray. Preparing the pan ahead of time ensures the muffins release easily after baking and makes cleanup much simpler.
Add the ripe avocados, eggs, monk fruit sweetener, almond milk, and vanilla extract to a blender or food processor. Blend until the mixture is completely smooth and creamy, with no visible avocado chunks remaining. This step is important for creating muffins with a moist, tender texture and ensuring the avocado blends seamlessly into the chocolate flavor.
In a large mixing bowl, whisk together the almond flour, unsweetened cocoa powder, baking powder, baking soda, ground cinnamon, and sea salt until evenly combined. Whisking the dry ingredients thoroughly helps distribute the leavening agents evenly and prevents lumps of cocoa powder in the batter.
Pour the blended avocado mixture into the bowl of dry ingredients. Using a rubber spatula or wooden spoon, gently stir until just combined and no dry streaks remain. Be careful not to overmix, as this can result in denser muffins. The batter should be thick, smooth, and rich in color.
If using, gently fold in the sugar-free chocolate chips and chopped walnuts until evenly distributed throughout the batter. The chocolate chips add pockets of melted chocolate, while the walnuts provide a pleasant crunch and additional texture.
Divide the batter evenly among the prepared muffin cups, filling each one approximately three-quarters full. This gives the muffins enough room to rise while baking without overflowing. For an extra-special touch, sprinkle a few additional chocolate chips or chopped walnuts over the tops before placing them in the oven.
Bake for 20–24 minutes, or until the tops spring back lightly when touched and a toothpick inserted into the center comes out with a few moist crumbs attached. Begin checking around the 20-minute mark, as baking times may vary depending on your oven. Avoid overbaking to maintain the muffins' soft and moist texture.
Remove the muffin tin from the oven and allow the muffins to cool in the pan for 10 minutes. This brief resting period helps them firm up slightly, making them easier to remove without breaking apart.
Carefully transfer the muffins to a wire cooling rack and allow them to cool completely. Cooling them on a rack prevents condensation from building underneath, helping preserve their tender texture.
Serve the muffins warm or at room temperature. Store any leftovers in an airtight container according to the storage recommendations, making them perfect for meal prep, quick breakfasts, or nourishing snacks throughout the week.