Preheat the oven to 350°. In a small bowl, soak the bread in the grape juice for 5 minutes, pressing to soften.
Spread the almonds in a pie plate and toast for 6 minutes, until lightly golden; let cool. Transfer 1 cup of the almonds to a blender. Add the bread, cucumber, apple, grapes, garlic, vinegar and 1/4 cup of olive oil. Puree until smooth. Strain the soup through a sieve into a bowl, pressing on the solids. Whisk in the buttermilk and season with salt and pepper. Refrigerate until chilled, at least 30 minutes.
Pour the gazpacho into cups and garnish with the mint and remaining 1/4 cup of almonds. Drizzle with olive oil and serve.