Preheat oven to 375°F. Wash and pat dry sweet potatoes. Pierce a few times with a knife. Wrap in foil. Place onto a baking sheet.
Place into oven. Bake for 45-55 minutes or until soft when squeezed.
Meanwhile, spread pecans on a separate baking sheet in a single layer. Toast while potatoes bake for 5-7 minutes, then set aside.
To assemble: Remove foil from potatoes. Slice potatoes down the middle leaving at least a ½ inch border on each end. Squeeze ends to open, leaving a gap in center. Place onto a baking pan, covered with foil spritzed with cooking spray for easier clean-up.
Divide butter between sweet potatoes. Season each with ¼ tsp salt. (May adjust salt to taste)
In a small bowl, mix together brown sugar and cinnamon. Sprinkle over butter. Use a fork to gently fluff through sweet potato flesh.
Divide toasted pecans between potatoes and top with marshmallows.
Return to the oven baking for 5 minutes or just until marshmallows are melting and golden. Broil for a few minutes to toast further, if desired.
Let stand for 5 minutes, then serve.