In a small bowl, combine the sugar and pumpkin pie spice. In a large bowl, combine the berries with half the lemon zest and lemon juice and half the sugar and spice mixture. Allow the berries to sit and macerate for 15 minutes. Slice each ciabatta loaf in half lengthwise and then slice each half in half on the bias. Brush the cut sides of the bread with the melted butter, sprinkle with the remaining sugar and spice mixture and place on the grill. Grill until toasted and browned, 3 to 4 minutes. Combine the remaining lemon zest with the whipped topping and stir. Remove the bread from the grill. Divide the bread evenly among 4 plates. Top each with 1/2 cup berry mixture. Serve with a dollop of the whipped topping and garnish with mint.