Preheat the oven to 425°F (220°C) and prepare a baking sheet by spraying it with non-stick cooking spray.
Season the chicken tenderloins on both sides with salt, pepper, and garlic powder.
In a bowl, mix together the breadcrumbs and grated parmesan cheese. Dip each chicken tenderloin into the egg mixture, letting excess drip off, then press it into the breadcrumb mixture to fully coat. Arrange the breaded chicken on the prepared baking sheet.
Lightly spray the tops of the breaded tenderloins with olive or avocado oil cooking spray. Bake for 8 minutes, then carefully turn the chicken over and bake for an additional 5 minutes.
Remove from the oven and spoon marinara sauce over each piece. Top each with a half slice of mozzarella cheese and return to the oven for 2–3 minutes, until the cheese melts.
Garnish with fresh or dried parsley and serve with extra marinara sauce if desired.