Preheat your oven to 350°F (175°C) and position a rack in the center. Lightly grease a 9x5-inch loaf pan and line with parchment paper, allowing some overhang on the sides for easy removal.
In a large bowl, whisk together the whole wheat flour, baking soda, baking powder, cinnamon, nutmeg, cloves, and salt.
In a separate medium bowl, whisk the eggs until lightly beaten. Add the maple syrup (or honey), melted coconut oil (or butter), applesauce, milk, and vanilla extract. Whisk until smooth and well combined.
Pour the wet ingredients into the dry ingredients and stir gently with a rubber spatula just until combined. Avoid over-mixing.
Fold in the diced apples and nuts (if using).
If using the streusel topping, combine the oats, whole wheat flour, brown sugar, and cinnamon in a small bowl. Cut in the cold butter using a fork or your fingertips until the mixture resembles coarse crumbs.
Transfer the batter to the prepared loaf pan and smooth the top with a spatula. If using, sprinkle the streusel topping evenly over the batter.
Bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean with just a few moist crumbs. If the top starts browning too quickly, tent loosely with aluminum foil after about 40 minutes.
Allow the bread to cool in the pan for 10 minutes, then use the parchment paper sling to lift it out onto a wire rack. Let it cool for at least 30 minutes before slicing.