Rinse the chicken breast under cold water to remove any juices from the packaging. Pat dry.
Coat each breast with the seasonings listed under the 'Chicken' section: garlic powder, salt, and pepper.
Slice each breast of chicken down the center from edge to edge, lengthwise, 3/4 of the way. Be careful to leave the ends uncut. You want to create a pocket in the center of the breast. Use your fingers to open up the chicken breast.
Place a nonstick, oven-safe pan over medium heat with butter. When the butter has melted, add the chopped spinach and cook until it has wilted.
As the spinach is cooking, add the remaining ingredients for the filling to a medium-sized mixing bowl.
Once the spinach has wilted, add the minced garlic and saute for 1-2 minutes. Remove from heat and add to the mixing bowl. Wipe pan with a paper towel to clean - you will use it to bake.
Mix the filling ingredients well to combine. Set aside.
Preheat oven to 375 degrees F.
To 3 separate dishes:
2. Eggs - whisked
3. Breadcrumbs, italian seasoning, parmesan cheese, salt, and pepper.
Start stuffing each breast with the filling. I find that it is best to hold the chicken breast like it's a pita pocket. Open the center of the breast as well (and carefully) as you can and stuff as much of the filling into each breast as you can. Close each breast with toothpicks.
Time to coat. First, dip the breast in the flour, then the whisked eggs (be sure to allow any excess to drip off), and then into the breadcrumbs mixture. Allow the breast to be fully coated in each dip - especially the breadcrumb mixture. It helps to use both hands to mold/pat the crumbs firmly into place.
Spray the same pan (or a baking dish) with nonstick cooking spray. Transfer each breast over to the pan, leaving a little room in between each to bake.
Allow to bake for 30-40 minutes or until the chicken temperature reaches 165 degrees F.
Remove from oven, add the cheese and then the marinara (or vise versa) to each breast. Place back into the oven to melt the cheese and warm the sauce. Keep an eye on it.
Remove and serve with your favorite pasta or vegetable side dish. Enjoy!