Place a chicken breast flat on a cutting board. Hold it steady with one hand and carefully slice it in half horizontally using a sharp knife to create two thin cutlets. Repeat with the second breast to make 4 pieces total.
Place the sliced chicken pieces in a large Ziploc bag. Pound each piece to an even ¼-inch thickness using a meat mallet or heavy skillet.
Set up a breading station with three shallow dishes. In the first, add the flour. In the second, beat the eggs with the milk. In the third, combine panko, Parmesan, Italian seasoning, garlic powder, salt, and pepper.
Dredge each chicken breast in the flour, shaking off excess. Dip into the egg mixture, then press into the breadcrumb mixture to coat evenly.
Heat vegetable oil in a large skillet over medium-high heat until hot.
Cook chicken until golden brown and cooked through, about 3–4 minutes per side. Work in batches if needed.
Transfer to a paper towel-lined plate to drain. Serve hot.
Notes
You can bake panko chicken on a wire rack at 425°F for 15–20 minutes, flipping halfway for even crispness if you prefer, instead of frying.