Heat oven to 350°F (177ºC) with rack set in middle position.
Coat a 8½ × 4½-inch loaf pan with nonstick spray. Line pan with parchment paper, leaving a 2-inch overhang on two sides.
Whisk together flour, baking soda, baking powder, ginger, salt and nutmeg; set aside.
In a separate bowl, whisk together sweet potato purée, eggs, sugar, buttermilk, oil, and rosemary.
Add flour mixture to sweet potato mixture and mix just until combined; fold in cranberries.
Scrape batter into prepared pan and smooth top.
Combine seeds, oats, turbinado sugar, and sea salt; sprinkle evenly over batter.
Bake bread until dark brown on top and a toothpick inserted in the center comes out clean, 55–65 minutes.
Let bread cool completely in pan set on a wire rack.