Preheat the grill to medium heat. Halve and pit the nectarines and, using a pastry brush, brush each cut side with about 1/4 teaspoon honey. Rub about 1/2 teaspoon of brown sugar into each side of the fruit.
Place the nectarines on the grill cut side down. Cover the grill and cook until the nectarines have grill marks, or about 5 minutes. Flip to the other side for 1 minute.
Remove from the grill and place on a plate cut side up. Allow to cool for 2-3 minutes, then fill the cavities with 1 tablespoon Nutella.
Top with a scoop of vanilla ice cream and whipped topping, if desired.
Sprinkle a tablespoon of pecans on top of the ice cream or whipped topping and garnish with a maraschino cherry.