Lightly grease a standard loaf tin and, if you like, line it with baking parchment to make removing the loaf easier, then preheat your oven to 180°C / 350°F / Gas mark 4.
Spoon the entire 500 ml tub of natural yogurt into a large mixing bowl, making sure to scrape out every bit so your measurements stay accurate.
Beat the egg lightly in a small bowl or jug, then pour it into the yogurt and whisk them together until the mixture looks smooth and uniform.
In a separate bowl, add the oats, baking powder and salt, stirring well so the baking powder and salt are evenly dispersed among the oats.
Tip the oat mixture into the bowl with the yogurt and egg, then stir slowly with a spatula or wooden spoon until everything is just combined and no dry patches remain.
Look at the mixture to ensure it is thick but spoonable, more like a heavy batter than a traditional bread dough, and let it sit for a couple of minutes so the oats begin to absorb the liquid.
Pour or spoon the mixture into the prepared loaf tin, smoothing the top with the back of a spoon or spatula so it is level and reaches into the corners.
Place the tin in the preheated oven and bake at 180°C / 350°F / Gas mark 4 for 30 minutes, allowing the loaf to rise and begin to set.
After 30 minutes, reduce the oven temperature to 150°C / 300°F and continue baking for a further 30 minutes until the loaf is firm to the touch and a skewer inserted into the centre comes out clean.
Remove the loaf from the oven, leave it in the tin for about 10 minutes, then lift it out onto a wire rack to cool completely before slicing into even pieces.