Preheat oven to 425° with rack set in upper third. Combine salt, pepper, chopped oregano, and lemon zest. Coat chicken with oregano mixture.
Heat oil in a large ovenproof frying pan over medium-high heat. Cook chicken skin side down until well browned, 10 to 12 minutes. Transfer chicken to a rimmed baking sheet and discard all but 1 tbsp. drippings. Return chicken to pan skin side up and surround with tomatoes, olives, and garlic, making sure to leave the skin uncovered.
Bake chicken until no longer pink in thickest part (cut to test), about 20 minutes.
Top chicken with feta and oregano leaves.