Heat half of the oil in a large skillet over medium-high heat.
Add chicken and brown until cooked through - about 5 minutes per side; remove from pan and keep
warm.
Heat remaining oil in the skillet; add onion, garlic, celery, zucchini, bell pepper and oregano; sauté for
2 minutes. Stir in tomatoes and rosemary; cook for 2 minutes. Stir in spinach, salt and pepper; cook
for 1 minute or until spinach wilts.
Serve sauce over chicken.