Preheat the oven to 400°F (200°C).
In a large oven-safe skillet, heat olive oil over medium-high heat.
Season the chicken thighs with salt, pepper, and oregano. Place them in the skillet, skin-side down.
Sear the chicken for about 5-7 minutes until golden brown. Flip and sear the other side for another 3-4 minutes.
Add minced garlic to the pan and sauté for 30 seconds until fragrant.
Pour in chicken broth, lemon juice, and add lemon zest, scraping the bottom of the skillet to release any flavor bits.
Add cherry tomatoes and spinach to the pan, stirring to combine all ingredients.
Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through.
Remove from oven and let it rest for about 5 minutes before serving.