Prepare the Marinara Sauce by heating olive oil in a saucepan. Add chopped onion and minced garlic, and sauté until onion is translucent. Add marinara sauce and simmer for 10-15 minutes.

Preheat the oven to 375°F (190°C). Pound the chicken breasts until ½ inch thick. Set up a breading station: beat an egg in one bowl and mix whole wheat breadcrumbs with salt and pepper in another. Dip chicken in egg, then coat with breadcrumbs.

Grease a baking sheet and place the breaded chicken breasts on it. Bake for 20-25 minutes, flipping halfway through, until golden brown and cooked through.

Remove chicken from oven and top each piece with marinara sauce, mozzarella cheese, and Parmesan cheese.

Return the assembled chicken to the oven and bake for another 10-15 minutes until the cheese is melted and bubbly.

Let the chicken rest for a few minutes before serving. Garnish with fresh basil and serve hot.