Heat grill to high. Melt the butter in a large saute pan on the grates of the grill. Whisk in the sugar and cook until melted and smooth. Standing back, carefully add the bourbon and cook for 2 minutes. Add 1/3 cup pecans and cook for 30 seconds. Add the bananas and spoon the sauce over the bananas constantly until softened, about 4 to 5 minutes.
Scoop the ice cream into bowls and top with the bananas and sauce. Garnish with the remaining chopped pecans and serve.