Toast 1 tsp each coriander and cumin seeds for 30 secs. Grind and stir into soup.
Put the cucumbers in a food processor with the yogurt, stock, garlic and mint, then season to taste. Blend until smooth, then pour into a jug. Place in the freezer for 20 mins to chill.
When ready to serve, heat the grill. Brush one side of the flatbread with 2 tsp olive oil, and grill for 1 min or until browned and crisp. 3 To serve, pour the soup into chilled bowls or glasses. Drizzle over the remaining olive oil and season with a little cracked black pepper. Serve with the crisp flatbread on the side.