Prep pan and oven. Position a rack in the center of your oven and preheat the oven to 350°F. Lightly grease a 8x4" inch loaf pan. I like to line mine with parchment paper as well and grease lightly again.
Make streusel. In a small mixing bowl, whisk together the flour, sugar, cinnamon and salt. Cut in the cold butter until a crumbly mixture forms. Set aside.
Combine Dry Ingredients. In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Combine wet ingredients. In a second mixing bowl, whisk together the oil, granulated sugar, brown sugar, eggs, vanilla, sweet potato, and orange juice.
Combine wet and dry ingredients. Make a well in the center of your dry ingredients and pour in the liquid ingredients. With a spatula, stir to combine until the last of the flour has been mixed in. Stop mixing at this point to avoid overmixing.
Bake the bread. Pour the batter into the pan. Sprinkle streusel over the bread. Bake the bread for 60-70 minutes, or until a cake tester or toothpick inserted in the center of the loaf comes out clean; and that same tester inserted about 1/2" into the top of the loaf doesn't encounter any totally unbaked batter. You should see moist crumbs, not raw batter. Mine was perfect at 60 minutes, so begin checking your bread at 60 minutes, but every oven is different so you may need additional time.
Cool the bread. Remove the bread from the oven, and cool it on a rack in the pan for 10 minutes. Remove from the pan and continue to cool. When it's completely cool, wrap it well in plastic wrap, and store it overnight before serving for best texture.
Make the glaze. In a small mixing bowl, whisk together the powdered sugar, milk, and vanilla. Drizzle over the cooled bread.