1. Preheat oven to 350 degrees Fahrenheit. Slice off the top of the head of garlic, just enough that the actual cloves are peeking out. Place the bulb on a piece of aluminum foil. Drizzle olive oil over the garlic and seal the foil. Place sealed garlic in baking pan, to avoid leaking, and roast for one hour.
2. While garlic is roasting, place two tablespoons olive oil in a six-quart pot over medium heat. Add leeks and onions; saute until golden brown. Browning longer will create a deeper flavor. Add zucchini to the pot. Add water, chicken soup mix and vegetable soup mix, or salt. Bring to a boil and cover.
3. Reduce heat, and simmer on low for 45 minutes. Remove the garlic from the oven and allow to cool. Pop out cloves directly into soup. Transfer soup to a blender and puree until smooth or use an immersion blender directly into the pot. Serve hot.
4. If there are leftovers, when reheating the soup, heat on low flame, just until warm.