Heat oven to 425°F. Set an oven-safe 12-inch skillet on the stove.
Pound chicken to even thickness. Pat dry, then season both sides with salt and pepper.
Set up three bowls: flour; beaten eggs; breadcrumbs mixed with Parmesan, Italian seasoning, garlic, and onion powder.
Dredge chicken in flour, shake off excess. Dip in egg, then press firmly into breadcrumb mixture.
Warm olive oil and butter over medium-high. Brown chicken until deep golden, 3–4 minutes per side.
Spoon a thin layer of marinara into the skillet. Nestle chicken on top and cover with remaining sauce.
Top with mozzarella and the extra Parmesan. Bake until cheese is bubbly and chicken hits 165°F, 10–12 minutes.
Broil 1–2 minutes for extra color if desired. Rest 5 minutes, then scatter basil and red pepper flakes.