Preheat your oven to 350°F (about 175°C) so it’s ready when you need it. In one bowl, whisk together the flour, sugar, baking soda, cinnamon, ginger, nutmeg, and salt until evenly mixed. In another bowl, beat the eggs and combine with pumpkin puree and vegetable oil until smooth.
Pour the wet mixture into the dry ingredients and stir gently until they are just combined—don’t overmix or the muffins may become tough. Then gently fold in the grated apple so it’s evenly distributed through the batter.
Mix the streusel topping ingredients (brown sugar, flour, cinnamon, melted butter) until crumbly. Scoop the muffin batter into lined or greased muffin tins, sprinkle the streusel on top, then bake in the preheated oven for 20-25 minutes until a toothpick inserted in the center comes out clean. Remove muffins from the tin and let them cool on a cooling rack before serving.