Preheat the oven to 400F.
(See recipe note about chicken size).
Pat the chicken dry with a paper towel. Drizzle with a touch of olive oil and sprinkle with oregano, salt, and pepper. Use your hands to rub the spices and oil all over the chicken.
In a large oven-proof skillet (12-inch cast iron works best), warm the oil over medium-high heat and tilt the pan so the oil coats the skillet. Once the oil is hot, place the chicken pieces into the skillet and cook until nicely browned, about 3 minutes. Flip and cook for 1 more minute. Turn off the heat.
Pour the marinara all over the chicken and give the pan a shake to distribute the sauce. If it’s not saucy enough or looks dry from the hot skillet, stir in a splash of water or more marinara (marinara brands can vary a lot in thickness).
Nestle bread chunks all around the chicken. You want the bread to soak up some sauce but also get crispy on top (the best part!), so make sure some bread is still poking out of the sauce. Sprinkle the cheese evenly all over.
Bake for 15-20 minutes or until the bread pieces are crisp on top, cheese is melting, and sauce is bubbly. Let the skillet rest for a few minutes, then serve topped with parmesan and basil, if using. See serving suggestions.