Quarter remaining strawberries and place in a large bowl.
Add greens, green onion, feta cheese, and half of walnuts and toss until mixed.
Whisk vinegar, sugar and salt in small bowl to blend. Whisk extra-virgin olive oil. Whisk in water, 2 tablespoons at a time. Mix in mashed strawberries. Season dressing with salt and pepper to taste
Pour over salad; toss to coat. Sprinkle remaining walnuts on top.