Preheat the oven to 350 degrees F.
In a shallow dish, mix the flour, garlic powder, salt, and pepper.
In a second shallow dish, whisk together the egg whites (or whole eggs) with 2 tbsp water.
Pour the seasoned breadcrumbs into a 3rd shallow dish.
Dredge the chicken in the flour mixture, shaking off any excess, then dip it into the egg mixture, and finally into the breadcrumbs. Shake off any excess breading, but ensure the breasts are well coated. Repeat with all the breasts.
Heat the oil in a large, seasoned cast-iron skillet over medium heat.
Sauté the chicken breasts until lightly golden on each side, about 3-4 minutes (1 ½- 2 minutes per side). Spray the breasts with a little extra olive oil spray, if needed, when flipping.
Transfer the skillet to the oven and bake for 20 minutes.
While the chicken is baking, warm the marinara in a saucepan over low-medium heat.
Top the chicken with the shredded parmesan and fontina and bake for 10 minutes more, until the cheese is melted and bubbly.
Drizzle each breast with 2 tbsp marinara and top with chopped fresh basil. Serve any extra sauce on the side.