Preheat oven to 325 degrees F.
Peel sweet potatoes and cut into 1-inch cubes.
Place sweet potato cubes in a medium saucepan and cover with water.
Cook over medium-high heat until tender.
Drain and mash.
In a large bowl, mix together mashed potatoes, maple syrup, brown sugar, eggs, salt, yogurt, vanilla and cinnamon.
Blend until smooth.
Pour into a 13-by-9 inch baking dish.
Topping: In a medium bowl, mix the brown sugar and oats.
Add in syrup, melted butter, salt and cinnamon; blend until mixture is coarse.
Stir in pecans.
Sprinkle over sweet potato mixture.
Bake 30 minutes, or until topping is lightly browned.