Preheat oven to 350°F. Rub sweet potatoes all over with oil. Place on parchment paper-lined baking sheet. Sprinkle sweet potatoes evenly with 1 teaspoon of the pumpkin pie spice. Bake 55 minutes or until tender. Cool sweet potatoes slightly.
Make a lengthwise slit along top of each sweet potato with small knife. Squeeze ends of each sweet potato towards the middle to push the flesh out of the top. Use a spoon to scoop the flesh, leaving enough in the skin to keep the shells intact. Mix sweet potato flesh, 3/4 cup of the yogurt, butter, brown sugar, remaining 1 teaspoon pumpkin pie spice and salt in medium bowl until well blended. Spoon mixture into sweet potato shells, mounding slightly. Gently press sides of sweet potatoes together.
Bake 10 to 15 minutes or until browned and heated through. Meanwhile, mix remaining 3/4 cup yogurt and orange extract. Serve sweet potatoes with dollop of yogurt mixture and a sprinkle of additional pumpkin pie spice.