Rinse the mixed greens, dry thoroughly and place the leaves in a large serving bowl. Cut the smoked chicken fillet into uniform cubes and set aside temporarily.
In a small bowl, combine the extra virgin olive oil, fresh lemon juice and Dijon mustard. Whisk this vigorously until a smooth dressing forms. Season with salt and freshly ground black pepper.
Halve the avocado and remove the pit. Scoop the flesh out of the skin with a spoon and cut into cubes the same size as the chicken. Add the sliced avocado and chicken cubes to the mixed greens in the bowl.
Pour the dressing over the salad and gently toss the ingredients so the avocado stays intact and everything is coated with a thin layer of dressing. Serve the chicken salad immediately.