Preheat the oven to 375°F (190°C).
Place each chicken breast between two sheets of plastic wrap and gently pound with a meat mallet or rolling pin until about 1/2 inch thick.
Set up three shallow bowls: one with the flour, one with the eggs beaten with 1 tablespoon water, and one with a mixture of breadcrumbs, grated Parmesan, garlic powder, dried oregano, salt, and black pepper.
Dredge each chicken breast first in the flour, shaking off excess, then dip into the egg mixture, and finally coat evenly with the breadcrumb mixture, pressing gently to adhere.
Heat olive oil in a large oven-safe skillet over medium heat. Add the breaded chicken breasts and cook until golden brown on both sides, about 3-4 minutes per side.
Remove the skillet from heat. Spoon marinara sauce evenly over each chicken breast.
Sprinkle shredded mozzarella cheese evenly on top of the sauce-covered chicken breasts.
Transfer the skillet to the preheated oven and bake until the chicken is cooked through and the cheese is melted and bubbly, about 20 minutes.
Remove from the oven and sprinkle with chopped fresh basil before serving.
To make ahead: Prepare the chicken through step 7, cover the skillet tightly with plastic wrap or foil, and refrigerate for up to 24 hours. When ready to serve, bake as directed in step 8.