Preheat a char-grill pan on medium. Lightly spray the chicken with oil and sprinkle with the sumac. Cook for 8 – 10 minutes or until lightly charred and cooked through.
Meanwhile, arrange the spinach, orange segments and celery on a serving plate. Combine 2 teaspoons of the reserved orange juice with the oil and garlic in a small bowl.
Thickly slice the chicken and add to the salad. Sprinkle with the almonds and drizzle the dressing over to serve.