To make ribbons: If you have a mandolin, thinly slice the zucchini and summer squash. If you do not have a mandolin, simply slice them as thin as you can by hand.
To make walnut pesto: Place a small sauté pan over medium heat. Add walnuts to the dry pan and cook for approximately 2 minutes, or until they start to become fragrant and are a light golden brown. Once the walnuts have cooled, add them to a food processor. Process until finely chopped. Next add basil and parmesan and process again until combined. Turn on processor and slowly add olive oil until the ingredients start to come together. Turn off processor and set aside.
To combine: Heat a large sauté pan over medium heat. Add water, zucchini and summer squash and gently sauté for approximately 4 minutes or until they are tender but still have a slight bite. Add 2 tablespoon of the pesto to the pan and sauté for 30 seconds more, just to combine. Serve immediately.