Grease an 8 X 8-inch microwave and oven proof glass baking dish with some coconut oil.
Layer in the sweet potato slices in oiled baking dish.
Mix 2 tablespoons coconut oil, brown and white sugars, orange zest, orange juice and salt in a one cup liquid measuring cup or small bowl.
Pour mixture over sweet potatoes. Tightly cover with saran wrap. Microwave for 10-12 minutes or until the potatoes are done. Let sit for a minute and carefully remove saran wrap. (Steam will escape and will be very hot. Be careful not to steam burn yourself).
Just before serving, top with marshmallows and bake on the top rack ( at least 4-5 inches away from the heat source) at a 450 degree oven for about 5-6 minutes or until the marshmallows are the color you like.