Preheat oven to 375 degrees and line a sheet pan with foil or parchment paper.
Start by making the spicy marinara. In a medium sauce pot, heat the olive oil over medium heat. Add the onion and cook until soft and translucent, about 3 minutes. Add the garlic and cook until fragrant, about 1 minute.
Next add the crushed tomatoes, tomato sauce, sugar, crushed red pepper flakes, Italian seasoning, dried parsley, salt, and pepper. Stir and then bring to a boil. Lower the heat, cover with a lid, and leave it at a low simmer while you prepare the chicken. Stir the marinara occasionally.
In one shallow bowl, whisk the eggs and water together. In a second shallow bowl, combine the Panko breadcrumbs, parmesan cheese, and dried parsley.
Dip the halved, and thinly pounded chicken breasts into the eggs and then dredge into the cheese-breadcrumb mixture. Press the chicken down firmly into the breadcrumbs so that the chicken is well coated and then place on a plate.
In a large skillet, add 1 tbsp of the butter and 1 tbsp of the olive oil over medium-high heat. When the butter has melted, add 2 of the chicken breasts. Let them cook for about 3-5 minutes before flipping. You want the chicken to have a nice golden crust. Flip them and then cook for another 2-4 minutes on the other side.
Place the cooked chicken breasts on the prepared sheet pan. Add the remaining butter and olive oil to the skillet and cook the remaining chicken breasts the same as the first half.
Once all of the chicken is cooked and on the sheet pan, ladle a healthy scoop of the marinara partially across the chicken. Top each cutlet with 1/4 cup of the shredded mozzarella cheese. Bake in the oven for about 10 minutes until the cheese is completely melted.
Top the chicken with chopped fresh parsley or basil. Serve alongside pasta (use the extra marinara to top) or vegetables. Enjoy!