Finely chop the onion and saute with olive oil and salt in a saucepan for 5-6 minutes until it becomes transparent.
Meanwhile cut the other vegetables in large pieces. Add to the pot along with the herbs, pepper, lemon zest and whole garlic cloves.
Saute for 5-6 more minutes until they have a nice smell and add the water or if you want, the vegetable broth or chicken.
Cook for 20-25 minutes until the vegetables are tender and when the soup cools down a bit, stir it in the blender on high speed until it becomes smooth and velvety. The soup will be quite thick so if you want it a little more thin, dilute water or broth and add as much lemon as you like.
Cut the sausage into thin diagonal slices and saute in dry nonstick pan until it becomes golden brown. Serve immediately the soup with a little olive oil and as much sausage as you like.