Lightly beat the eggs with the sugar, then add the oil and yoghurt. Mix in the oats and rest while you’re making the blueberry sauce.
Put the blueberries in a small saucepan, add the sugar, lemon juice and vanilla. Bring to the boil, then cook until you get a thick, sticky sauce (almost jam-like). Turn off the heat and let it cool.
Preheat the oven to 180°C. Line a muffin-tin with paper case or put some silicon cases on a baking tray.
Add the flour and baking powder to the oat mixture, combine well. Spoon half of the batter into the muffin cases - they should be half full - then spoon some blueberry sauce on top, then cover with the remaining batter. If you want the muffins to be crunchy, top them with a pinch (or two) of muscovado sugar.
Bake the muffins in the middle of the oven for 20-25 minutes, until golden brown.
Remove the tin from the oven, let the muffins cool in the tin for 5 minutes, then transfer them to a cooling rack.