Preheat the oven to 350°F (175°C) and grease a cake pan.
In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
In a separate bowl, mix brown sugar, oil, pumpkin puree, apple sauce, and vanilla extract.
Add dry ingredients to the wet ingredients, alternating with almond milk. Stir until smooth.
Fold in the chopped apples (optional).
Pour the batter into the prepared pan.
If using, combine streusel ingredients and sprinkle over the top.
Bake for 35-40 minutes or until a toothpick inserted comes out clean.
Let the cake cool before serving.