Heat grill. It works better to use wood or a mixture of wood and charcoal. I haven’t tried this on the gas side of the grill.
Melt 1 TBS butter. Mix 1 TBS brown sugar and 1/2 TBS cinnamon.
Wash sweet potatoes and towel dry. It is okay if they are still damp. Brush or roll potatoes in melted butter. Roll potatoes in cinnamon-sugar. Wrap tightly in foil.
Once the fire has died down throw the foil wrapped potatoes near the edge of the coals. Cook until they become soft. It can take between 20-40 minutes depending on the how hot the coals are. I start checking after 10 minutes.
Either allow potatoes to cool or rinse foil wrapped potatoes under cold water until it is cool enough to handle.
If the potatoes are still warm turn broiler and allow to warm while assembling. If not heat oven to 400.
Grease a baking dish with butter. Scrap potatoes into baking dish. Add remaining butter, cinnamon, and sugar. Mix well. Add pineapples and nuts. Top with marshmallows.
Put potatoes in oven until marshmallows are a toasty brown. I prefer to use broil setting.