Light a campfire and let it burn down to hot coals, or preheat a grill or camp stove to medium-high.
In a small bowl, whisk together the melted butter, maple syrup, cinnamon, and salt. If using cayenne, add it now.
Brush the pineapple rings generously with the glaze on both sides.
Place the rings directly on the grill grate or in a lightly oiled skillet. Cook for 4-5 minutes per side, until grill marks appear and the pineapple is caramelized and tender.
Remove from heat and brush with any remaining glaze. Serve warm as a side with grilled meats, or as a dessert with a dollop of yogurt or ice cream.