Preheat oven to 350°F.
Bring potatoes to a boil in a large Dutch oven filled with water. Reduce heat; simmer 20 minutes. Drain; return to pan. Add 1 tablespoon brown sugar, rind, juice, 1/2 teaspoon turmeric, vanilla, salt, egg whites, and milk; mash. Spoon into a 2-quart baking dish coated with cooking spray.
Combine flour, remaining 1/4 cup brown sugar, oats, pumpkin seeds, and butter in a bowl. Stir in remaining 1/2 teaspoon turmeric and ginger. Sprinkle oat mixture over potato mixture. Bake at 350°F for 40 minutes.
