Preheat the oven to 450°F. Toss together the tomatoes, feta cheese, olives, garlic, pine nuts, and vinegar.
Rub the chicken with olive oil, salt, and pepper. Using a small, sharp knife, carefully cut a slit along the thick part of each chicken breast, creating a pocket. Add enough stuffing to fill each pocket and transfer the chicken to a baking sheet.
Bake for 15 minutes. Top with any remaining stuffing.
A different take on stuffed chicken.