Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper for easier removal.
In a medium bowl, mix together the flour, baking soda, baking powder, salt, cinnamon, and nutmeg. Set aside.
In a large mixing bowl, combine the pumpkin puree, vegetable oil, and granulated sugar. Whisk until smooth.
Add the eggs and vanilla extract to the pumpkin mixture, whisking until completely blended.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Be careful not to overmix. If using, fold in the chopped walnuts at this stage.
In a separate small bowl, prepare the streusel topping by combining rolled oats, brown sugar, flour, cinnamon, and melted butter. Mix until crumbly.
Pour the pumpkin bread batter into the prepared loaf pan. Sprinkle the streusel mixture evenly on top.
Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, allow the bread to cool in the pan for 10-15 minutes before transferring it to a wire rack to cool completely.
Notes
Serve warm or at room temperature, optionally drizzling with a light glaze made from powdered sugar and a splash of milk for extra sweetness. Enjoy with a cup of coffee or tea!