Preheat your oven to 400°F (200°C).
In a large oven-safe skillet, heat the olive oil over medium heat.
Season the chicken breasts with salt, pepper, and oregano.
Sear the chicken breasts in the skillet for about 5 minutes on each side, until golden brown.
Add minced garlic to the skillet and sauté for 1 minute, until fragrant.
Pour in the lemon juice and add the zest, cherry tomatoes, and spinach to the skillet.
Transfer the skillet to the preheated oven and roast for about 20 minutes, or until the chicken is cooked through.
Remove the skillet from the oven and let it rest for a few minutes before serving.