Pull or cut the curly leaves off of the stem, discarding the stems. Rinse kale in large bowl of cold water. Dry with salad spinner or paper towels. Chop the kale into 1/2 inch pieces and place in large salad bowl.
In a medium mixing bowl, combine the red onion, lemon peel, lemon juice, water, mustard, agave or honey, pepper and salt. Using a wire whisk, slowly drizzle in the olive oil while mixing to emulsify. Drizzle 4 tablespoons of dressing over kale. Using clean hands, massage the kale for 1 minute or until it begins to wilt. (The combination of the acid from the lemon juice, salt and heat of your hands will tenderize the kale leaves.) Taste and add more dressing as needed. (You will have some dressing left over; store in the refrigerator up to 1 week.) Add the oranges, strawberries, and walnuts to the kale mixture; toss to coat.