Preheat oven to 350°F (180°C). Line a standard 12-cup muffin tin with paper liners.
In a medium bowl or large measuring cup, whisk together the plant milk, maple syrup, olive oil, vanilla, and lemon juice.
In a large mixing bowl, whisk together the oat flour, all-purpose flour, almond meal, rolled oats, flaxseed, baking powder, baking soda, cinnamon, and salt.
Pour the wet mixture into the dry ingredients and stir until just combined - do not overmix. Leave the batter to rest for 5 minutes to firm up, then gently fold in the blueberries.
Divide the batter evenly into the prepared muffin cups, filling each about ¾ full. If you like, press a few extra blueberries on top.
In a small bowl, stir together the streusel flour, oats, sugar, and almond meal. Add the olive oil or vegan butter and mix with a fork until crumbly.
Spoon the streusel mixture evenly over each muffin.
Bake for 23–26 minutes, or until a toothpick inserted in the center comes out clean.
Let muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely.