Preheat the grill to high.
Heat one tablespoon of the oil in a pan and gently fry the spring onions for 2-3 minutes, or until softened. Add the wine and simmer for 5-6 minutes, or until the liquid has reduced by half.
Stir in the stock, bring to the boil and add the rocket and lettuce. Reduce the heat and simmer for 3-4 minutes, stir in the cream and season, to taste, with salt and freshly ground black pepper. Blend until smooth with a stick blender.
Drizzle the remaining oil over the slice of bread, scatter the garlic over and toast under the grill until golden-brown and crisp.
To serve, return the soup to the pan to warm through if needed, then ladle into a serving bowl and serve with the garlic crouton. Garnish with rocket leaves and chopped mint leaves.