Preheat oven to 400 degrees F. Butter a 9”x 9” baking dish and set aside.
Slice each yam into thin slices, stopping about 3/4 of the way through. Place each one onto a foil lined baking sheet.
Combine butter, salt, spices, and lemon zest. Spread butter mixture over the yams. Cover with foil and bake in preheated oven for 40 minutes. Uncover and baste the yams. Return to oven and continue cooking another 15 minutes.
Top with marshmallows and pecans, pushing some between the slices. Place under the broiler until marshmallows are golden.