Greek-Style Chicken with Pickled Onions, Tomatoes, and Tzatziki

Chicken breasts, boneless skinless

English cucumber

Grape or cherry tomatoes

Lemon, zest

Oregano, dried

Parsley, fresh leaves

Red onion, medium

White rice, Cooked long-grain

Salt and ground pepper, Coarse

Olive oil, extra-virgin

Red-wine vinegar

Greek yogurt, nonfat plain