Heat in a deep saucepan over medium heat vegetable oil, add chopped onion and garlic and fry for 2-3 minutes.

Add the chopped zucchini and the Basil leaves, pour water (or broth), add salt and pepper to taste. Bring on high heat to a boil, cover, reduce the heat and cook for 15-20 minutes until tender zucchini.

Grind the soup with the immersion blender, still slightly warm and remove from heat. Serve with croutons and fresh Basil. Optionally, flavoring natural yogurt or sour cream.