Instructions. Preheat the oven to 190°C/gas 5. Put 12 large muffin cases into a muffin tray. Preheat the oven to 350F. Toss the cubed apples with a ½ teaspoon of cinnamon and keep aside. These moist muffins are studded with fresh apples and applesauce, making it a favorite for everyone. Treat yourself to Apple-Oatmeal Muffins for a breakfast-on-the-go or afternoon snack. In a large bowl, thoroughly combine both flours, the oats, baking powder, cinnamon and sugar. Liberally grease a muffin pan with nonstick spray.