Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with parchment paper liners.
Dice your Granny Smith apple into small, uniform pieces (approximately 1/4 inch cubes).
In a small saucepan, melt the tablespoon of butter over medium heat. Add the diced apple, cinnamon, nutmeg, ginger, and water. Cook for 3-5 minutes until the apples slightly soften but maintain their structure. Remove from heat and let cool.
In a large mixing bowl, whisk together the almond flour, monk fruit sweetener, baking powder, baking soda, and salt until evenly combined.
In a separate medium bowl, beat the eggs until slightly frothy (about 30 seconds), then add the almond milk, melted coconut oil, apple cider vinegar, and vanilla extract. Whisk until completely incorporated.
Pour the wet ingredients into the dry ingredient bowl. Using a spatula, gently fold the mixture together until just combined. Be careful not to overmix.
Gently fold in the cooled apple spice mixture until evenly distributed throughout the batter.
If making the streusel topping, combine the almond flour, crushed nuts, monk fruit sweetener, cold cubed butter, and cinnamon in a small bowl. Use your fingertips to work the butter into the dry ingredients until the mixture resembles coarse crumbs.
Fill each muffin cup about 3/4 full with batter. If using the streusel topping, sprinkle a generous amount over each muffin.
Bake in the preheated oven for 22-25 minutes, or until a toothpick inserted into the center comes out clean and the tops are golden brown. For evenly baked muffins, rotate the pan halfway through baking time.
Allow to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.