Preheat oven to 350° F
Pour frozen sweet potatoes in pan with 1 cup of water (just follow instructions on bag)
Stir for a good 8-10 minutes until creamy
Add brown sugar and butter and stir until melted
Pour mixture into greased casserole dish
Sprinkle pecans over top, followed by marshmallows.
Bake for 30 minutes or until marshmallows turn golden brown