Preheat the oven to 400 degrees F (200 degrees C).

Toss chicken, potatoes, bell peppers, onion, oil, and garlic together in a large bowl until well combined. Transfer mixture to a large sheet pan and spread into a single layer. Squeeze lemon wedges over top, then place spent wedges onto the sheet pan. Sprinkle oregano over top, then season with salt and pepper. Add Kalamata olives.

Bake in the preheated oven until potatoes are fork-tender and chicken breasts are no longer pink in the center and the juices run clear, about 25 minutes. An instant-read thermometer inserted into the center of chicken breasts should read at least 165 degrees F (74 degrees C).