In a large mixing bowl, whisk the flax meal with the water. Set this aside while you gather the rest of the ingredients (about 5 minutes).
Preheat your oven to 425°F (220°C) and line or lightly grease a muffin tin.
In the large bowl with the flax mixture, mash the ripe bananas until smooth using a potato masher or fork.
Add the rest of the wet ingredients (oil, brown sugar, milk, and vanilla) and stir until well combined.
Sprinkle all of the dry ingredients (almond flour, flour, oats, baking powder, ground cinnamon, and salt) over top. Mix the dry and wet ingredients just until a muffin batter forms.
Scoop a half cup of batter into each of the muffin cups (the batter should dome slightly out of the cups of the tin).
Sprinkle each muffin with about a ½ teaspoon of turbinado sugar and a few oats.
Bake the muffins at 425°F (220°C) for 7 minutes, then decrease the temperature to 350°F (175°C) for 25-27 minutes.
When the muffins have finished baking, remove them from the oven and allow to cool for at least 20 minutes before gently freeing them from the muffin pan.
Store leftover muffins in a bread bag or under a tea towel for the first day or two to keep the sugar oat topping crispy. You can then keep your muffins in an airtight container at room temperature for up to 3 more days. They will also keep in the freezer for up to 3 months.