In a large salad bowl combine the greens, mushrooms, fennel, carrots, celery, artichokes, olives, and scallion, and toss the mixture to combine. Pat the chicken dry and season with the thyme, salt, and pepper. In a large nonstick skillet set over moderately high heat, warm the oil until hot, add the chicken, and saute it for 2 minutes. Turn and cook for 1 minute more. Transfer the chicken to a plate. Add the wine to the skillet and reduce it by half. Add the broth, whisk in the mustard, and return the chicken to the skillet. Simmer 2 to 3 minutes, or until the chicken is cooked through and springy to the touch. Transfer the chicken to a plate, reduce the remaining liquid to 1/2 cup, and pour it into a small bowl. Make the dressing: Add the olive oil, whisking, to the bowl of reduced cooking liquid and whisk in the vinegar and salt and pepper, to taste. Cut chicken into slices and add to the salad bowl. Pour juices from plate into dressing, whisking to combine, and drizzle over salad. Toss mixture until chicken and vegetables are well coated with dressing.