Start by prepping your chicken. Place your chicken breasts or tenderloins in a large ziploc bag, 2-3 at a time. Using the flat side of a meat mallet (or side of a can or other heavy object), begin to flatten your meat.
After you flatten your meat, cut the pieces into similar sizes. I usually cut one large chicken breast in half after flattening.
Before cooking the chicken, you need to get your dredging station ready. Get out 2 low wide bowls or pie pans. In the first, crack 2 eggs and add 1-2 tablespoons of water. Whisk those together and set aside (I set it near my stovetop).
In another low, wide bowl, mix together Panko bread crumbs, dry grated Parmesan cheese, Italian seasoning, and salt. Set next to the egg mixture, near the stove top.
Next, prep your baking dish and oven. Turn the oven to 350°F. Get out a 9x13" baking dish (or other wide, rimmed baking dish) and spray with cooking spray. Set aside.
In a large saucepan or heavy-bottomed pan, pour flavorless oil until it's about 1 inch up the side of the pan. Depending on your pan size, the amount will vary.
Heat oil to a medium-high heat, until a sprinkle of water dropped in sizzles (will take about 5 minutes to heat up).
Once oil is hot, dredge your first 3 pieces of chicken, first by dipping in the egg mixture, and then into the breadcrumb mixture. Then carefully set each piece of dredged chicken into the hot oil, using tongs.
Let cook on each side for about 5-7 minutes. Each piece will take a different amount of time depending on the size and thickness. Once one side is browned and cooked, flip with tongs. Once chicken looks cooked, tap on the center with the back of the tongs, if it feels firm it's probably cooked through. If you want to be sure, you can double check by making a slight cut with a sharp knife to ensure it's cooked.
Once first batch is cooked through, remove and place in the prepared baking dish. If the oil starts to get too hot, you can turn it down to medium heat.
Once you start another batch of chicken, add a little more oil into the pan. Continue cooking until all the chicken is done. Place all chicken in prepared baking dish. Cover each piece of chicken with a couple spoonfuls of marinara sauce and then top with fresh Parmesan cheese.
Bake in preheated 350°F oven for 10-15 minutes until cheese melts and sauce is warmed through.