Preheat the oven to 425F. Place oven racks so one is in the upper third, and one is in the lower third.
Spread the panko crumbs on a baking sheet. Drizzle with 3 tbsp olive oil and sprinkle with ½ tsp salt. Toss and spread into an even layer. Bake for 8–10 minutes, stirring halfway through, until golden brown. Let it cool down.
In a large bowl, combine the toasted panko, chopped parsley, 1 cup of the grated Parmesan, and garlic powder. Mix well.
Wipe off the baking sheet. Drizzle the remaining 2 tbsp of olive oil between two baking sheets and brush to coat evenly.
In one shallow bowl, whisk the eggs. In another shallow bowl, add the flour.
Pat the chicken dry with paper towels. Season both sides with the remaining salt and black pepper.
Dredge the chicken cutlets in flour and shake off the excess. Dip into the egg, letting extra drip off, and then press into the panko mixture, coating well. Place the coated chicken in a single layer on the oiled baking sheets.
Bake for 8 minutes, then flip the chicken, rotate the pans between racks, and bake another 6–9 minutes until fully cooked through.
Remove from the oven and turn the oven to broil. Spoon about ¼ cup of marinara over each piece of chicken. Top with sliced mozzarella and sprinkle with the remaining Parmesan.
Broil on the top rack for 5–8 minutes, until the cheese is melted and bubbly.
Sprinkle with freshly chopped basil before serving.