Heat oven to 180°C (350°F) and fold a 20 cm (7.9 inches) loaf pan with parchment paper or grease with oil.
Add the oats to a high speed blender and process for 20-30 seconds, until finely ground into flour. Skip this step if you use oat flour.
Transfer the oat flour into a large mixing bowl, then quickly stir with baking powder and salt.
In a separate bowl, mix all wet ingredients together: egg, whole-milk yogurt, olive oil and optionally apple cider vinegar (for a softer homemade oat bread).
Using a spatula, make a hole in the center of the flour and add the wet mixture into the middle. Mix until dry and wet ingredients are well combined into a lump-free batter.
Evenly spread the batter into your prepared loaf pan. Bake in hot oven for 30 to 40 minutes, or until a toothpick inserted into the center of your oatmeal bread comes out clean. Let cool for at least 15 minutes before slicing.