Cut the smoked chicken breast into even cubes with a sharp knife. Halve the avocado, remove the pit and scoop the flesh from the skin. Cut the avocado half into cubes roughly the same size as the chicken. Break the walnuts by hand into coarse pieces.
Get a large mixing bowl and add the mixed greens. Add the chicken cubes, avocado pieces and broken walnuts to the bowl with the greens. Gently toss together, so the avocado stays intact and all ingredients are well distributed.
Make the dressing by mixing the tablespoon of olive oil in a small bowl with the lemon juice. Whisk together briefly with a fork or spoon. Pour the mixture over the salad and toss everything once more lightly for even flavor distribution.
Divide the prepared chicken salad over a flat plate or transfer it to a deep bowl. Serve the dish immediately to preserve the crispness of the mixed greens and prevent discoloration of the avocado.