Begin by preheating your oven to 350°F (175°C). Prepare a muffin tin by lining it with paper liners or lightly greasing each cup with cooking spray or oil.
In a large mixing bowl, combine the whole wheat flour, baking powder, baking soda, ground cinnamon, and salt. Whisk them together thoroughly until the dry ingredients are well incorporated.
In a separate mixing bowl, combine the mashed bananas, applesauce, honey (or maple syrup), eggs, and vanilla extract. Use a fork or whisk to blend this mixture until it reaches a smooth consistency.
Pour the wet mixture into the bowl containing the dry ingredients. Gently stir with a spatula or wooden spoon until just combined; take care not to overmix to ensure a light muffin texture.
Carefully fold in the diced apples, rolled oats, and if desired, the chopped walnuts and raisins or cranberries. Make sure these additions are well distributed throughout the batter without vigorous mixing.
Use a scoop or spoon to divide the batter evenly among the muffin cups, filling each one approximately three-quarters full to allow for rising.
Transfer the muffin tin to the preheated oven and bake for 18-22 minutes. To check for doneness, insert a toothpick into the center of a muffin; it should come out clean or with a few moist crumbs attached.
Once baked, allow the muffins to cool in the pan for about 5 minutes, then carefully transfer them to a wire rack to cool completely.
Notes
Serve warm with a sprinkle of cinnamon and a slice of apple on the side.