Cut the chicken breast into small cubes. Preheat a skillet, add 1 tablespoon of extra-virgin olive oil and chicken cubes. At medium heat, fry until cubed chicken is coooked to your likeness, usually 7-10 minutes. Turn the cubes occasionally.
To prepare the dressing, zest half an orange and combine with mustard, olive oil, salt, black pepper, and pressed garlic. Whisk until smooth. Set the dressing aside.
Plate the spinach leaves, diced celery, apple wedges, chopped onion, and pecans. Place the chicken cubes on top of the greens and drizzle the dressing over the salad.
Garnish with pieces of orange, if desired.