For the dressing: In a food processor, combine the apple, vinegar, lemon juice, maple syrup, olive oil, salt, and pepper. Blend until smooth.
Place the lettuce, avocado, and walnuts in a large bowl. Add 3/4 of the dressing and toss until all the ingredients are coated. Arrange in a single layer on a platter and top with the smoked salmon. Drizzle with the remaining dressing and serve.
Cook's Note: To toast the walnuts, arrange in a single layer on a baking sheet. Bake in a preheated 350 degrees F oven for 6 to 8 minutes until lightly toasted. Cool completely before using.
Recipe courtesy of Giada De Laurentiis