In medium bowl, soak bread cubes in ½ cup cold water; set aside.
In blender, pulse cucumber, grapes, almonds, garlic, 1 ½ cups cold water, and 1 ½ teaspoons salt until finely chopped. Add soaked bread; puree until smooth. Pulse in vinegar and ¼ cup olive oil. Refrigerate until cold, at least 4 hours or up to 24 hours.
With box grater set in large bowl, grate tomatoes. Discard skins. To tomato pulp, add remaining 2 tablespoons oil and pinch salt. To serve, divide gazpacho among bowls. Garnish with additional oil and chopped almonds, if desired. Spoon tomato mixture onto toasts. Serve with gazpacho.
