Slice each breast horizontally into 2 pieces. This allows the chicken to cook faster.
Season each slice with salt and pepper.
Combine panko crumbs and the fresh Parmesan cheese in a small bowl.
Coat the chicken with the bread crumb mixture pressing gently to adhere. Set the chicken aside on a plate.
Heat 2-3 tablespoons of olive oil in a large, oven-safe skillet over medium-high heat.
Add the chicken breast and cook 3-4 minutes on each side until golden brown and cooked through. Remove the cooked chicken to a plate then pour half of the prepared pasta sauce onto the bottom of the pan.
Gently lay the chicken on top of the sauce.
Top each piece of chicken with a couple tablespoons of sauce, ¼ cup chopped spinach, and two tablespoons of the grated mozzarella cheese.
Place the pan under the broiler for 2-4 minutes until cheese just begins to show browned patches, then serve immediately.