Spray an 8x8 or 9x9 pan with nonstick spray. Set aside. Preheat oven to 350 degrees F.
Peel sweet potatoes and dice into 1/2-inch chunks. Add to a large stock pot and cover with water. Bring potatoes to a boil and cook for 10 to 15 minutes, until fork tender. Drain potatoes
Return the potatoes to the stock pot and mash well. Stir in butter, granulated sugar, salt, cinnamon and egg. Spread into the prepared baking dish.
In a large bowl, stir together brown sugar, flour, pecans, rolled oats, salt and cinnamon. Drizzle in melted butter and stir until combined and crumbly. Spread over the mashed sweet potatoes. Bake for 20 to 25 minutes, until golden.