Preheat the oven to 375 degrees. Coat a small baking dish with cooking spray.
Place the peeled & sliced sweet potatoes in a pan of cold water then bring to a boil over medium-high heat. Reduce heat and simmer until fork-tender, about 20 minutes. Drain the sweet potatoes well. Add the brown sugar, butter, cinnamon, and salt then mash together using a potato masher until creamy and smooth. Taste and add more seasonings, to taste, if needed.
Spread the sweet potatoes in the prepared baking dish evenly. Sprinkle the top with the chopped pecans.
Spread the miniature marshmallows evenly over the top. Place into the oven and bake for 22-25 minutes, or until the marshmallows are golden brown. Remove from the oven and serve. Enjoy.