Preheat oven to 375 degrees.
In a small bowl, mix together cinnamon, brown sugar, and salt.
Put softened butter on a piece of plastic wrap. Use your hands to mix in cinnamon mixture. Form butter into a rectangle, wrap with plastic wrap and place in freezer for 20-30 minutes.
Make oatmeal mixture by combining oats, brown sugar, cinnamon, salt, and butter in a small bowl. Use your fingers to bring the mixture together.
With a sharp knife, make thin cuts into the sweet potatoes, about 1/4 inch each. Stop about 1/2 inch from the bottom of the potato to hold the potato together.
Take the butter out of the freezer and in small chunks, place the butter between the slices of potato.
Place the oatmeal mixture on top of the potato and place potatoes on a foil lined baking sheet.
Bake for 30 minutes, then cover with foil and bake for another 20 minutes, or until potatoes are cooked through.