Preheat the oven to 400°F (200°C). Lightly grease a baking sheet with olive oil or line it with parchment paper.
In a shallow bowl, combine the whole wheat breadcrumbs, grated Parmesan cheese, dried Italian seasoning, garlic powder, salt, and black pepper.
In another shallow bowl, whisk together the egg and water until well combined.
Pound each chicken breast to an even thickness of about 1/2 inch using a meat mallet or rolling pin between two sheets of plastic wrap.
Dip each chicken breast first into the egg mixture, allowing excess to drip off, then coat evenly with the breadcrumb mixture. Press the breadcrumbs onto the chicken to adhere well.
Place the coated chicken breasts on the prepared baking sheet. Drizzle the olive oil evenly over the chicken breasts to help them crisp up.
Bake the chicken in the preheated oven for 15 minutes.
Remove the baking sheet from the oven and spoon 1/4 cup marinara sauce over each chicken breast.
Sprinkle 1 ounce shredded part-skim mozzarella cheese evenly on top of the sauce on each breast.
Return the baking sheet to the oven and bake for an additional 8-10 minutes, or until the chicken is cooked through (internal temperature of 165°F or 74°C) and the cheese is melted and bubbly.
Remove from oven and let rest for 5 minutes before serving.
Garnish with fresh basil leaves if desired and serve warm.