Preheat the oven to 400°F (200°C).
In a small bowl, whisk together the balsamic vinegar, honey, Dijon mustard, minced garlic, oregano, thyme, salt, and pepper.
In a large oven-safe skillet, heat olive oil over medium-high heat. Season the chicken thighs with salt and pepper, then add them to the skillet. Sear the chicken for about 5 minutes on each side until golden brown.
Pour the balsamic mixture over the chicken in the skillet. Add the cherry tomatoes around the chicken.
Transfer the skillet to the preheated oven and bake for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C).
In the last 5 minutes of baking, add the fresh spinach to the skillet and stir gently to combine.
Remove from the oven and let it rest for a few minutes. Garnish with fresh basil if desired before serving.