Make sure your oven rack is centered, then heat to 425.
Lightly grease a 12-cup muffin tin with avocado oil, then dust with flour, tapping out excess flour.
In a medium bowl, mix the topping together, set aside.
In a small bowl, mix the flaxseed meal with the room temperature water. Rest for 10 minutes to thicken.
In a medium bowl (large enough to fit all wet ingredients), mix the oat milk with the lemon juice. Rest for 10 minutes.
In a large bowl, mix together the flour, cane sugar, 1/4 cup brown sugar, baking powder, baking soda, salt, and ground cinnamon.
Once the milk + lemon and flax mixtures have rested for 10 minutes, add the flax mixture to the milk, along with the oil, melted butter, vanilla, almond extract, and ginger. Mix thoroughly.
Gently fold the wet mixture into the dry mixture until just combined. Do not over-mix. DO NOT ADD THE BLUEBERRIES YET.
Add about a tablespoon of batter to each muffin cup.
Now gently fold the frozen (not thawed) blueberries into the batter. Fill the muffin tin to the top.
Sprinkle the walnut sugar mixture on top.
Bake for 6 minutes.
Reduce the heat to 350—DO NOT OPEN THE OVEN—then bake the muffins for another 18 minutes, or until a sharp knife inserted into the center comes out clean.
Let the muffins partially cool in the tin for 5 minutes on a cooling rack, then carefully remove the muffins and continue to cool. Store leftover, cooled muffins in an airtight container for two to three days.