For the dressing:
For the spiced nuts:
To make the dressing, place the berries in a food processor or blender and puree until smooth. Pour the mixture through a fine mesh sieve, pressing out as much fruit puree as possible while removing the seeds. In a liquid measuring cup or jar, combine the blackberry puree with the vinegar, honey, and olive oil. Whisk vigorously until the mixture is well blended and smooth. Season with salt and pepper to taste. Chill until ready to use.
To make the spiced nuts, melt the butter in a medium skillet over medium heat. Stir in the brown sugar, cinnamon, ginger, cayenne, and salt and pepper to taste. Allow the mixture to heat for about 1 minute, then stir in the chopped nuts. Let cook, stirring occasionally, until the nuts are lightly toasted, about 5 minutes. Remove from the heat and let cool.
To serve, plate portions of salad greens on salad plates. Top with crumbled goat cheese, fresh blackberries, vidalia onion and the spiced nuts as desired. Drizzle lightly with the blackberry vinaigrette. Serve immediately.