In a bowl, whisk together balsamic vinegar, honey, olive oil, minced garlic, oregano, salt, and pepper. Add the chicken breasts to the marinade and let them sit for at least 30 minutes (or up to 2 hours in the fridge for more flavor).
Preheat your oven to 400°F (200°C). Take a large oven-safe skillet and place it on medium-high heat.
Remove the chicken from the marinade, reserving the marinade for later. Add the chicken to the skillet and sear for about 4-5 minutes on each side until golden brown. Remove the chicken from the skillet and set aside.
In the same skillet, add the halved cherry tomatoes and cook them for about 2 minutes until they begin to soften.
Return the chicken to the skillet and pour over the reserved marinade. Scatter fresh spinach around the chicken and tomatoes.
Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C).
Remove from the oven and garnish with fresh basil. Serve hot, spooning the balsamic sauce and tomatoes over the chicken.
Notes
For more flavor, marinate the chicken for up to 2 hours.