Preheat the oven to 400°F (200°C).
Butterfly each large chicken breast and cut so you have 4 cutlets total; place between two sheets of plastic wrap and pound to an even thickness of about 1/4–1/2 inch.
Season both sides of each cutlet with salt and pepper.
In one shallow bowl, beat the eggs. In a second shallow bowl, combine the Italian breadcrumbs, panko and 3/4 cup of the grated Parmesan.
Heat the olive oil in a large oven-safe skillet over medium-high heat; add the minced garlic and cook 2–3 minutes until fragrant but not browned.
Dredge each cutlet first in the beaten eggs, then press into the breadcrumb-Parmesan mixture to coat evenly.
Working in the hot skillet, cook the breaded cutlets 3–4 minutes per side until golden and almost cooked through; add more oil if needed. Remove the cutlets from the skillet and turn off the heat.
Pour half the jar of marinara sauce into the bottom of the skillet and stir to loosen any browned bits and garlic.
Return the cutlets to the skillet on top of the sauce. Spoon a little extra sauce over each cutlet, then top each with two slices of mozzarella, the remaining grated Parmesan, and the sliced basil.
Bake in the preheated oven 10–12 minutes, until the cheese is melted and beginning to brown and the chicken is cooked through.
Serve the chicken Parmesan over spaghetti with crusty bread if desired.