Preheat the oven to 400°F (200°C). Lightly oil a shallow baking dish large enough to hold the chicken in a single layer.
Trim any fat from the chicken breasts and slice thicker pieces horizontally to make even thicknesses about 1/2 inch; if needed, place between plastic wrap and gently pound to an even 1/2-inch thickness.
Set up a three-bowl dredging station: in one bowl whisk the flour with 1/2 tsp salt and 1/4 tsp pepper; in another bowl beat the eggs until smooth; in a third bowl combine panko, grated Parmesan, lemon zest, garlic powder and remaining salt and pepper.
Working one piece at a time, coat each chicken breast in the seasoned flour, shake off excess, dip into the beaten eggs, then press firmly into the panko-Parmesan mixture so it adheres evenly on both sides.
Heat 2 tablespoons olive oil in a large ovenproof skillet over medium-high heat. When shimmering, add 2 pieces of breaded chicken and cook 2 to 3 minutes per side until the crust is golden (you’re not cooking through—just setting the crust). Transfer seared pieces to the prepared baking dish and repeat with remaining chicken, adding a little more oil if needed.
Spoon about 1/4 cup marinara over each breast, then sprinkle shredded mozzarella evenly across the top. If you like a little heat, scatter a pinch of crushed red pepper flakes over the sauce.
Bake uncovered in the preheated oven for 15 to 18 minutes, or until the chicken reaches 165°F (74°C) and the cheese is melted and bubbling. For a browned top, switch to broil for 1 to 2 minutes—watch carefully so it doesn’t burn.
Remove from oven and let rest 5 minutes. Sprinkle fresh basil or parsley on top before serving. Serve the chicken over pasta, rice, or a bed of steamed vegetables.