Heat oven to 400°F.
Scrub potatoes clean and dry with a dishtowel. Slice each potato in half lengthwise. Rub on all sides with oil and place, cut-side down on a sheet pan. Sprinkle the peels of the potatoes with some salt.
Transfer the sheet pan to the oven and roast the potatoes until they can be easily pierced with a fork, 25 to 30 minutes.
Remove the potatoes and use tongs to flip them over so the cut-side is facing up. Let them cool for a few minutes.
While the potatoes cool, heat the butter in the microwave just until melted (use the defrost button which will keep the butter from overheating as it melts).
Stir brown sugar, cinnamon, and salt into the melted butter.
Working carefully (the potatoes will still be hot; I find it helpful to hold them steady with a dishtowel in one hand), take a fork and scrape / mash the flesh of the potato, leaving the skin intact.
Spoon the butter mixture over the flesh of the potatoes and go back with your fork, gently combining the mixture with the sweet potatoes.
Press mini marshmallows into the potatoes. Scatter chopped pecans over the tops so that some fall between the marshmallows.
Return the potatoes to the oven and continue baking until marshmallows are very soft and golden brown, 10 to 12 minutes.