For nuts: Wrap a baking sheet with foil and spray with nonstick cooking spray. Add Vanilla Bean Sugar, water, cinnamon and allspice to a large saucepan over medium-high heat. Bring to a boil, then simmer until reduced by half, about 5 to 10 min., until mixture starts looking dark and thick. Quickly stir walnuts into the simmering syrup. Cook nuts in the syrup while stirring until it begins to bubble and thicken. Spread sugared nuts in a single layer on the prepared baking sheet, breaking up large clusters with a wooden spoon. Let cool completely, about 5 to 10 min., until the syrup dries.
For bananas: Preheat grill to medium-high and make sure it is clean and well oiled. In a medium bowl, mix sugar, cinnamon and allspice until thoroughly blended. Slice bananas in half lengthwise. Do not remove the peel. Lay bananas skin side down and generously sprinkle the flesh side of the bananas with the sugar mixture. Lightly rub sugar mixture onto bananas with your fingers to make sure as much of it sticks as possible. Repeat until all bananas are coated. Place bananas on the grill flesh side down and cook until the sugar starts to caramelize and nice grill marks appear. Turn bananas over and finish cooking flesh side up until the skin starts to fall away from the banana. This way you’ll get a soft, sugared banana that’s not burnt. If you grill the bananas in batches, be sure to brush the grill with more oil so the sugared bananas won’t stick.
Break nuts apart and serve over grilled banana halves (1 or 2 per person). You can keep the bananas in the skin and scoop bites out with a spoon. Drizzle the combo with any remaining syrup you may have from the nut mixture. Delicious with vanilla ice cream.