Preheat the oven to 350°F (180°C).

Cut off the top of the head of garlic, wrap the bulb in aluminium foil, and roast it on a baking sheet for 30 to 40 minutes, until tender. Allow the bulb to cool and then squeeze the garlic pulp out of the husks. This should yield 2 tablespoons or more of roasted garlic. Set aside.

Heat the oil over medium-high heat in a large saucepan. Add the green onions, red onion, and 1/4 teaspoon of salt and sauté for 5 minutes, until the onions are translucent. Add the celery, zucchini, and parsley and sauté for 5 minutes more.

Stir in the roasted garlic and the vegetable broth. Increase the heat to high and bring just to a boil. Reduce the heat to medium and simmer for 10 minutes. Add the spinach and simmer for 5 minutes more, until the leaves are just tender.

Remove the saucepan from the heat and allow the soup to cool somewhat. Stir in the nuts.

Pour the soup into your blender in batches, and puree on high for 30 to 60 seconds until smooth and creamy.

Return the soup to the saucepan and warm over medium-low heat. Season to taste with salt and pepper and serve.