Preheat the oven to 450 degrees F (232 degrees C).

Pat the chicken breasts dry. Season both sides with salt and pepper. Cut a slit in each chicken breast horizontally, creating a pocket. Set aside.

Place the spinach into a large bowl. Steam the spinach in the microwave for 2-3 minutes, until wilted. (Alternatively, saute on the stove for 3-5 minutes, until wilted.) Set aside to cool until it’s not too hot to handle.

Meanwhile, in a large bowl, mash together the softened cream cheese and garlic. (If you forgot to soften the cream cheese, you can microwave it to soften it.) Stir in 1/2 cup of mozzarella cheese.

When the spinach is cool enough to handle, squeeze over the sink to release as much water as possible. Stir into the cream cheese mixture.

Stuff the spinach mixture evenly into the chicken breasts. Use toothpicks, positioned horizontally, to secure the filling inside the pockets.

Heat the olive oil in a large (at least 12-inch) cast iron skillet over medium-high heat, until shimmering. Add the chicken and sear for 4-5 minutes per side, until golden brown on both sides.

Working quickly, top each piece of chicken with 2 tomato slices and 2 tablespoons of shredded mozzarella cheese.

Transfer spinach stuffed chicken breast to the oven. Bake for about 15 minutes, until the internal temperature reaches 165 degrees F (74 degrees C). (Make sure your meat thermometer is inserted into the chicken and not the filling to check the temperature.) If the cheese is not as dark as you like, place under the broiler for 1-3 minutes – this is optional.