Preheat the oven to 400 degrees F (200 degrees C). Place chicken breasts into a 9x13-inch baking dish.

Whisk olive oil, garlic, lemon juice, lemon zest, oregano, salt, and pepper together in a bowl. Brush some of the mixture onto chicken.

Place potatoes, bell pepper, onion, and lemon slices into a bowl; pour in remaining lemon juice mixture and toss to coat. Arrange vegetables and lemon slices around chicken in the baking dish.

Bake in the preheated oven for 30 minutes. Brush chicken and vegetables with the pan drippings. Continue to bake until chicken is browned, the juices run clear, and an instant-read meat thermometer inserted into the thickest part of a breast reads at least 165 degrees F (74 degrees C), about 30 more minutes.