Preheat the oven to 175c. Line a baking sheet with parchment paper. Line 8 muffin cups with paper liners.
MAKE THE CRUMBLE: In a small bowl, whisk together the flour, oil, and maple syrup until the mixture comes together. Crumble onto the baking sheet and bake for 20 minutes, or until the streusel begins to crisp up. Remove and set aside, but keep the oven on at 175c
MAKE THE MUFFINS: In a large bowl, whisk together the flour, baking soda, and salt. In a separate bowl, combine the eggs, coconut oil, maple syrup, lemon zest and juice, and vanilla. A little at a time, add the dry ingredients to the wet, stirring until a smooth batter forms.
Divide the batter among the 8 lined muffin cups, filling each ¾ of the way. Top each muffin with a few blueberries, and lightly swirl them into the batter with a spoon. Sprinkle the streusel topping over the muffins.
Bake for about 25 minutes, until the streusel is golden brown. Remove the muffins from the tin, set on a rack, and allow to cool completely. Store for up to 5 days in a sealed container, or for up to 2 months in the freezer. Defrost before reheating in a low oven.
NOTE: Blueberry is a classic, but you can swap in any berries or stone fruit in this recipe. If the fruit is very juicy or watery, like strawberries, bake for an extra 5 minutes.