Heat a frying pan over medium high heat with olive oil. Add minced garlic and chicken breasts. Season with salt and pepper and sear each side of chicken for 1-2 minutes. Remove from pan and add to baking dish.
In a bowl, mix together crushed tomatoes, dried basil, dried oregano, and season with salt and pepper. Pour sauce overtop of chicken breasts in baking dish.
In the last 5 minutes of baking, remove pan from oven and push the spinach into the sauce and sprinkle mozzarella cheese overtop. Add back to the oven.
Bake chicken for a total 25-35 minutes, or until chicken reaches 165°F when poked in the center with a meat thermometer.